Skip to Quick Glance, Deeper Details, ante, anti**, auto, bi, bio, co**, counter, de, dis, extra, -fold, geo, hydro, hyper, hypo, infra, inter, intra, macro, mega, meta, micro, mid, mini, mis, multi, neo*, non, over, para, post*, pre**, pro**, proto, pseudo, re, semi*, socio, sub, super, supra, trans, tri, ultra, un, under, -war.

Quick glance

Usually, do not hyphenate prefixes that are found in the dictionary (with many exceptions).

dislike, rearrange, unnecessary

With double vowels:

For CMS, generally hyphenate prefixes that cause a-a and i-i
(also de-e for some reason, but not ree or pree).

meta-analysis, anti-inflammatory, but neoorthodox
de-emphasize, but reenact and preelection

For AP, generally hyphenate prefixes that cause double vowels: a-a, e-e, i-i, o-o.

meta-analysis, anti-inflammatory, neo-orthodox
de-emphasize, re-enact, pre-election

With hyphenated compounds

non-open-minded

With open compounds (2+ words)

post–high school, anti–Civil War (CMS uses an en dash.)

post-high school, anti-Civil War (AP uses a hyphen.)

If not in dictionary:

CMS: Follow same pattern: midsentence

AP: Hyphenate it: mid-sentence

For words in the dictionaries, here are the usual patterns for forming them:

anteword

antiword for CMS / antiword and anti-word for AP (varies, see list below)
anti-iword, anti-Cap

autoword

biword

bioword

coword for CMS / co-word and coword for AP (varies, see list below)
co-oword except cooperate and coordinate in all forms, co-Cap

counterword, counterrword

deword, de-eword, de-Cap

disword, dissword

hyperword
hyperrword for CMS / hyper-rword for AP

hypoword

infraword

interword, interrword, inter-Cap

intraword, intra-aword

macroword

megaword

metaword, meta-aword

microword
microoword for CMS, micro-oword for AP except microorganism

midword, middword, mid-Cap
mid-2017, mid-1990s
his mid-forties for CMS /
his mid-40s for AP
the mid-twentieth century, but
mid-twentieth-century design for CMS /
the mid-20th century, but
mid-20th-century design for AP

miniword

misword, mishword, missword

multiword, multi-iword

neoword
neooword for CMS / neo-oword for AP
neo-Cap or Neo-Cap (varies, see list below)

nonword, nonnword, non-Cap, non–Compound Cap*

overword, overrword

paraword, para-aword

postword
posttword for CMS / post-tword for AP
post-Cap, post–Compound Cap*

preword
preeword for CMS / pre-eword for AP
pre-Cap, pre–Compound Cap*

proword with exceptions for CMS / proword but pro-cause for AP
pro-Cap, pro–Compound Cap*

protoword

pseudoword

reword
reeword for CMS / re-eword for AP
rereword, re-cover vs. recover, etc.

semiword, semi-iword

socioword

subword, subbword

superword
superrword for CMS / super-rword for AP

supraword, supra-Cap

transword, transsword, trans-Cap

triword

ultraword

unword, un-Cap

underword, underrword

prewar, postwar
prowar for CMS / pro-war for AP
antiwar for CMS / anti-war for AP

*For prefix–Compound Cap words such as pre–Civil War, use an en dash for CMS, but a hyphen for AP.

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Deeper details

Default prefix rules

Usually, do not hyphenate

subtopic, multiethnic

unless

1) unless it creates double vowels. CMS and AP differ on this issue.

CMS:

unless it creates a double a or i or might be misread

a-a: intra-arterial, meta-analysis
i-i: anti-inflammatory
ee: preeminent, reeducate
oo: cooperate, coordinate

might be misread: co-own

Exception:
de-e words are hyphenated (but ree, pree, etc. are not).

de-emphasize, but reeducate, preeminent

AP:

unless it creates a double of the same vowel.

a-a: meta-analysis
e-e: de-emphasize, pre-eminent, re-educate*
i-i: anti-inflammatory
o-o: co-own (BUT exceptions are cooperate and coordinate)

Exceptions:
cooperate and coordinate are the only two exceptions AP lists.
(But I have seen other exceptions, such as microorganism.)

de-e, pre-e, re-e: AP chooses to hyphenate all de-e, pre-e, and re-e words, disagreeing with WNW.

anti-: AP chooses to hyphenate most anti- words except for a small list.

2) unless the following word is capitalized.
mid-August

3) unless the prefix is doubled.
sub-subtopic

4) unless it conflicts with an existing word.
resign: to quit. re-sign: to sign again

If it’s not in the dictionary

Sometimes you will make up your own temporary term using a prefix (nonteachers/non-teachers). Or you might use a prefix term you’ve heard before, but it’s not necessarily a dictionary term (midsentence/mid-sentence). Sometimes terms like these eventually make it into the dictionary.

CMS: If it’s not in the dictionary, follow above pattern of rules. (Use Merriam-Webster’s Collegiate, 11th edition, abbreviated here as MW11.)

AP: If it’s not in the dictionary, hyphenate it. (Use Webster’s New World College, 5th edition, abbreviated here as WNW.)

Note: AP is not always consistent on this. Often its Q&A section answers with its default rule: “Because it is not in the WNW dictionary, hyphenate it.” But sometimes it says, “Based on similar words in WNW, do not hyphenate this one.” Other times it says, “A search of AP articles reveals a preference for no hyphen.”

Best approach if it’s not in the WNW dictionary and you don’t have access to AP Stylebook’s Q&A online: Hyphenate unless you usually see it with no hyphen or you know of a preference for no hyphen.

Are there exceptions?

Yes, many. I combed the two dictionaries and two style guides, and I listed all exceptions on this page.

For most prefixes, there are only a few exceptions and conflicts between dictionaries and style guides.
*But for anti, co, neo, post, pre, pro, and semi, the number of conflicts and odd terms require a table to illustrate.
**For anti, co, pre, and pro, AP has its own set of rules that conflict with WNW.

Special prefix rules

With compound terms

with hyphenated compounds:

non-web-related, non-life-threatening

with open compounds:

CMS uses an en dash. (CMS 6.80, 7.85)

pre–Civil War post–high school

AP uses a hyphen.

pre-Civil War post-high school

In titles and headlines, do you capitalize the word after the hyphen? (Title Case / Headline Style)

CMS: Capitalize it only if they could both stand alone as words:

Team Co-owner Speaks
President-Elect Speaks

AP: Don’t capitalize the letter after the hyphen.

Team Co-owner Speaks
President-elect Speaks

Note: AP officially prefers sentence-style capitalization for news headlines, but some publications prefer Title Case.

How are you supposed to know if it’s in the dictionary?

Good question. All you can do to be sure is buy the official dictionary or at least the app.

• There are common prefix words that you just know would be in the dictionary, but they’re not, such as relist/re-list.
• Then there are words you would assume would never be in the dictionary, but they are, such as cyberpunk (listed in both dictionaries).
• Then there are common words that appear in only one dictionary, such as minibar or preprint (both in MW11 only) or cyberattack (in WNW only).

MW11 lists far more prefix words than WNW.

ante

before, in front of

anteword

Examples: antebellum, antedate, anteroom

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary at a glance.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

ante meridiem, —————, ante-post

WNW

ante meridiem but antemeridian (both mean a.m.), ——–

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

anti

opposite, against, prevent

antiword for CMS / anti-word except small list of antiwords for AP (see table below)
anti-iword, anti-Cap

Examples

antiword: anticlimactic, antipollution (but AP disagrees with many of these, see table)
anti-iword: anti-intellectual
anti-Cap: anti-American

Exceptions/odd: Many. See table below.

AP disagrees with its dictionary for anti!

For AP, hyphenate all anti- words except this specific list (peach background in table below) and “physics terms.”

(Note: AP’s Ask the Editor considers terms such as antibacterial to fall under the physics category. I’ve noted these Ask the Editor terms in the table with ^.)

Table below includes all exceptions and odd terms, plus a selection of normal ones.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP has its own rules for anti!
Usually antiword anti-iword anti-Cap If not in MW11 dictionary, apply same rules: antiword	Usually antiword anti-iword anti-Cap If not in WNW dictionary, hyphenate: anti-unlisted	Usually anti-word except specific list of antiword exceptions (peach background). Usually differs from WNW dictionary!
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	AP agrees w WNW / AP disagrees w WNW / specific antiword exceptions listed in AP / exception to normal rule or odd / ^ = mentioned in Ask the Editor
antiabortion	antiabortion	anti-abortion
antiacne	anti-acne	anti-acne
antiaging	anti-aging	anti-aging
anti-AIDS	anti-AIDS	anti-AIDS
antiaircraft	antiaircraft	anti-aircraft
antialcohol	anti-alcohol	anti-alcohol
antiallergy	anti-allergy	anti-allergy
anti-American	anti-American	anti-American
antianxiety	anti-anxiety	anti-anxiety
anti-art	anti-art	anti-art
antiasthma	anti-asthma	anti-asthma
antibacterial	antibacterial	antibacterial ^
antibiotic	antibiotic	antibiotic
antibody	antibody	antibody
antibusing	antibusing	anti-busing
anticancer	anti-cancer	anti-cancer
antichoice	anti-choice	anti-choice
Antichrist (n.)	antichrist (n.)	Antichrist (n.); but anti-Christ (adj.)
anti-Christian	anti-Christian	anti-Christian
anticlimactic	anticlimactic	anticlimactic
anticlimax	anticlimax	anticlimax
antidemocratic	antidemocratic	anti-democratic
antidepressant	antidepressant	antidepressant
antidote	antidote	antidote
antidumping	anti-dumping	anti-dumping
antieconomic	anti-economic	anti-economic
antielitist	anti-elitist	anti-elitist
antiestablishment	anti-establishment	anti-establishment
anti-federalist	antifederalist	anti-federalist
antiflu	anti-flu	anti-flu
antifreeze	antifreeze	antifreeze
antifungal	antifungal	antifungal ^
antigen	antigen	antigen
antiglare	anti-glare	anti-glare
antigravity	antigravity	anti-gravity
antihero	antihero	antihero ^
antihistamine	antihistamine	antihistamine
anti-icing	anti-icing	anti-icing
anti-idiotype	anti-idiotype	anti-idiotype
anti-immigration	anti-immigration	anti-immigration
anti-imperialism	anti-imperialism	anti-imperialism
anti-inflammatory	anti-inflammatory	anti-inflammatory
anti-inflation	anti-inflation	anti-inflation
anti-intellectual	anti-intellectual	anti-intellectual
antiknock	antiknock	antiknock
antilabor	antilabor	anti-labor
antilock	anti-lock	anti-lock
antimatter	antimatter	antimatter
antimicrobial	antimicrobial	antimicrobial ^
antimissile	antimissile	anti-missile
antimodern	anti-modern	anti-modern
antinausea	anti-nausea	anti-nausea
anti-Nazi	anti-Nazi	anti-Nazi
antinuclear	anti-nuclear or antinuclear*	anti-nuclear
antioxidant	antioxidant	antioxidant^
antimony	antimony	antimony
antiparticle	antiparticle	antiparticle**
antipasto	antipasto	antipasto
antiperspirant	antiperspirant	antiperspirant
antiphon	antiphon	antiphon
antiphony	antiphony	antiphony
antipiracy	anti-piracy	anti-piracy
antipollution	antipollution	antipollution
antiproton	antiproton	antiproton**
antipsychotic	antipsychotic	antipsychotic
antiretroviral	antiretroviral	antiretroviral ^
anti-roll bar	antiroll bar	anti-roll bar
anti-Semitism, anti-Semite, anti-Semitic	anti-Semitism, anti-Semite, anti-Semitic	anti-Semitism, anti-Semite, anti-Semitic
antiseptic	antiseptic	antiseptic
antiserum	antiserum	antiserum
antislavery	antislavery	anti-slavery
antismoking	antismoking	anti-smoking
antisocial	antisocial	anti-social
antispam	anti-spam	anti-spam
antispyware	anti-spyware	anti-spyware
antisway bar	anti-sway bar	anti-sway bar
antitax	anti-tax	anti-tax
antitheft	anti-theft	anti-theft
antithesis	antithesis	antithesis
antitoxin	antitoxin	antitoxin
antitrust	antitrust	antitrust
antitussive	antitussive	antitussive
antiulcer	anti-ulcer	anti-ulcer
antiunion	anti-union	anti-union
antiuniverse	anti-universe	anti-universe
antiuniversity	anti-university	anti-university
anti-utopia	anti-utopia	anti-utopia
antiviral	antiviral	antiviral ^ anti-viral ^ (two different answers in Q&A. One compared it to the tech term anti-virus, another considered it a science term.)
antivirus	anti-virus	anti-virus
antiwar	antiwar or anti-war	anti-war

*or=both are equal variants, neither is preferred, per WNW.
**and “similar terms from physics” get no hyphen.
^ Not in AP’s list of unhyphenated, but APStylebook.com’s Ask the Editor said at least once not to hyphenate.

auto

of oneself, self-acting

autoword

Examples: autobiography, autofocus, autopilot

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11/CMS

auto-da-fé, ———-, Autoharp, Automat, Auto-Tune (secondary variant: auto-tune)

WNW/AP

auto-da-fé, auto-dial, autoharp, automat, ————

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional AP notes

automaker is one word (dictionaries agree).
autopilot for generic term, including airplane-related, but Autopilot for Tesla Inc.’s semi-autonomous driving system.
Auto Train is Amtrak’s rail service for carrying people and their cars.
autoworker is one word for generic term (dictionaries agree), but United Auto Workers for the union.

bi

two

biword

Examples: biathlete, bilateral, bisexual

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11/CMS

————-, bifold, bi-level

WNW/AP

bi-bivalent, bi-fold, bi-level

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional notes: bi vs. semi

AP notes that semiannual and biannual both mean twice a year. (But biennial means every two years.)

Despite that fact, semimonthly means twice a month, but bimonthly means every other month.

Semiweekly means twice a week in MW11. But biweekly is listed in MW11 with two definitions: twice a week and every two weeks, and WNW says biweekly means every two weeks, but “now rare” usage considers it twice a week. WNW states semiweekly is the preferred term for twice a week.

Arrgh! If you use these terms, please make it clear exactly what you mean.

bio

life, of living things

bioword

Examples: biochemistry, bioethics, biohazard

Exceptions/odd: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

co

with, together

coword for CMS / co-word and coword for AP (varies, see list below)
co-oword except cooperate and coordinate in all forms
co-Cap

Examples:

coword: for CMS, coworker, coauthor, coexist, but for AP, co-worker, co-author, but coexist
co-oword: co-op, co-own
but cooperate, cooperation, coordinate, coordinator, etc.
co-Cap: co-CEO

Exceptions/odd: Many. See table below.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Table below includes all exceptions and odd terms, plus a selection of normal ones. Gray, light blue, light pink: Not listed in this dictionary, so default rule applied.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP has its own rules for co!
Usually coword co-oword except cooperate and coordinate in all forms co-Cap If not in MW11 dictionary, apply same rules: counlisted.	Usually coword co-oword except cooperate and coordinate in all forms co-Cap if not in WNW dictionary, hyphenate: co-unlisted.	co-word for occupation or status words, but coword for others co-oword except cooperate and coordinate in all forms co-Cap
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	AP agrees w WNW / AP disagrees w WNW / co-word for occupation or status words / exception to normal rule or odd / ^ = mentioned in Ask the Editor
coanchor	co-anchor	co-anchor
coauthor	coauthor	co-author
coaxial	coaxial	coaxial
co-brand	co-brand	co-brand or cobrand ^
co-CEO	co-CEO	co-CEO ^
cochair	co-chair	co-chair
cochairman, cochairwoman, cochairperson	co-chairman, co-chairwoman, co-chairperson	co-chairman, co-chairwoman, co-chairperson
cocurricular	co-curricular	cocurricular ^
codefendant	codefendant	co-defendant
codependent	codependent or co-dependent	co-dependent ^
codetermination	co-determination	codetermination ?
coed	coed or co-ed	coed
coeducational	coeducational	coeducational
coedit, coedited	co-edit, co-edited	co-edit, co-edited
co-edition	co-edition	co-edition (probably)
coeditor	co-editor	co-editor
coefficient	coefficient	coefficient
coenzyme	coenzyme	coenzyme
coequal	coequal	coequal
coevolution, coevolve	coevolution, coevolve	coevolution, coevolve
coexist	coexist	coexist
coexistence	coexistence	coexistence
cofacilitator	co-facilitator	co-facilitator ^
cofounder	co-founder	co-founder
cohost	co-host	co-host
cohabit, cohabitation	cohabit, cohabitation	cohabit, cohabitation
coincidence	coincidence	coincidence
coinfection	co-infection	coinfection
coinsurance	coinsurance	coinsurance
colead, coleader	co-lead, co-leader	co-lead, co-leader ^
colocate	co-locate	co-locate, co-location ^
commingle	commingle	commingle (often misspelled)
commiserate	commiserate	commiserate
co-occur, co-occurrence	co-occur, co-occurrence	co-occur, co-occurrence
co-official	co-official	co-official
co-op	co-op	co-op ^
cooperate	cooperate	cooperate
cooperation	cooperation	cooperation
cooperative	cooperative	cooperative
co-opt, co-opted, co-option, co-optive	co-opt	co-opt
coordinate	coordinate	coordinate
coordination	coordination	coordination
coordinator	coordinator	coordinator ^
co-organizer	co-organizer	co-organizer
co-own	co-own	co-own
co-owner	co-owner	co-owner
copartner	copartner	co-partner
co-pay	co-pay	copay
co-payment	co-payment	copayment
copilot	copilot	co-pilot
copresident	co-president	co-president
coproduce	co-produce	co-produce ^
coproducer	co-producer	co-producer ^
coproduct	co-product	coproduct ^
coproduction	co-production	coproduction ^
copublisher	co-publisher	co-publisher
corelation	co-relation	co-relation
corespondent (in a divorce suit)	corespondent	co-respondent
correspondent	correspondent	correspondent
cosign, cosigner	cosign, cosigner	co-sign, co-signer
cosponsor	cosponsor	co-sponsor
costar	costar	co-star
coworker	co-worker or coworker	co-worker
coworking	co-working	co-working ^
cowrite, cowriter, cowritten	co-write, co-writer, co-written	co-write, co-writer, co-written

counter

opposite, a reaction against

counterword, counterrword

Examples

counterword: counterargument, counterclockwise
counterrword: counterrevolution

Exceptions/odd

MW11 and WNW list the same odd term:

counterreformation, but Counter-Reformation for the Roman Catholic reform movement.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

de

do the opposite of, remove

deword, de-eword, de-Cap

Examples

deword: deactivate, dehumanize, deindustrialize, deoxidize, deregulate
de-eword: de-emphasize, de-escalate
de-Cap: de-Stalinization

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

deaccession, deice

WNW

de-accession, de-ice

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

dis

opposite of, absence of, not

disword, dissword

Examples

disword: disappear, disfavor, disuse
dissword: dissatisfied, dissimilar

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Back to top. Skip to ante , anti**, auto , bi , bio , co**, counter , de , dis , extra , -fold , geo , hydro , hyper , hypo , infra , inter , intra , macro , mega , meta , micro , mid , mini , mis , multi , neo*, non , over , para , post*, pre**, pro**, proto , pseudo , re , semi*, socio , sub , super , supra , trans , tri , ultra , un , under , -war .

extra

outside, beyond

extraword

Examples: extracurricular, extramarital, extraordinary, extrasensory

Exceptions in both dictionaries

extra-base hit, extra-virgin

CMS and AP additional notes

CMS also lists extra-administrative, which is not in the dictionary, and varies from the typical style. No extra-awords are listed in either dictionary, so this example likely intends to show a preference for hyphenating extra-awords.

AP agrees with WNW but also notes that this rule applies when extra means “outside of.” It reminds us to use a hyphen when “extra” is part of an adjective meaning “more than usual,” as in extra-large shirt, extra-strong drink. The other authorities would either agree or leave out the hyphen altogether depending on context.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

-fold

multiplied by a number of times

numberfold

Examples: fourfold, tenfold, hundredfold

CMS and AP additional notes

CMS agrees with MW11, but also says to spell out or use digits based on CMS numbering style, so:

twenty-five-fold (which conflicts with AP)
150-fold

AP agrees with WNW, but notes the following:

AP’s Ask the Editor mentions “a hundredfold” as the best wording.

AP also offers these additional answers:

fifteenfold
twentyfold
twenty-fivefold (which conflicts with CMS)
a thousandfold

AP encourages rephrasing awkward constructions, e.g., 4.5 times, 500 times.

If not in dictionary

-fold words will not all be in the dictionary, so follow the above patterns.

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geo

earth, soil

geoword

Examples: geochemical, geochronological, geomagnetic, geometric

Exceptions: None

CMS and AP additional notes

AP specifically mentions geolocation and geotagging, neither of which are in the two dictionaries.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

back to top. Skip to ante , anti**, auto , bi , bio , co**, counter , de , dis , extra , -fold , geo , hydro , hyper , hypo , infra , inter , intra , macro , mega , meta , micro , mid , mini , mis , multi , neo*, non , over , para , post*, pre**, pro**, proto , pseudo , re , semi*, socio , sub , super , supra , trans , tri , ultra , un , under , -war .

hydro

water, liquid, or containing hydrogen

hydroword

Examples: hydroelectric, hydroplane, hydrospace

Exceptions: None

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Back to top. Skip to ante , anti**, auto , bi , bio , co**, counter , de , dis , extra , -fold , geo , hydro , hyper , hypo , infra , inter , intra , macro , mega , meta , micro , mid , mini , mis , multi , neo*, non , over , para , post*, pre**, pro**, proto , pseudo , re , semi*, socio , sub , super , supra , trans , tri , ultra , un , under , -war .

hyper

excessively, extremely

hyperword
hyperrword for CMS / hyper-rword for AP*

Examples

hyperword: hyperactive, hyperextend, hyperinflation

*About hyperrwords / hyper-rwords

*MW11 lists several hyperrwords, which are not hyphenated.
hyperrational, hyperresponsive, hyperromantic.

WNW does not list any, so for AP, hyphenate hyper-rwords by default rule.
hyper-rational, hyper-responsive, hyper-romantic.

Exceptions: None

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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hypo

beneath, less than

hypoword

Examples: hypoallergenic, hypomania, hyposensitize

Exceptions: None

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Back to top. Skip to ante , anti**, auto , bi , bio , co**, counter , de , dis , extra , -fold , geo , hydro , hyper , hypo , infra , inter , intra , macro , mega , meta , micro , mid , mini , mis , multi , neo*, non , over , para , post*, pre**, pro**, proto , pseudo , re , semi*, socio , sub , super , supra , trans , tri , ultra , un , under , -war .

infra

below, within

infraword

Examples: infrahuman, infrared, infrastructure

Odd terms / exceptions in both dictionaries

infra dig

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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inter

between, among

interword, interrword, inter-Cap

Examples

interword: interfaith, intermarriage, international, interoffice
interrword: interracial, interrelate
inter-Cap: inter-American

Odd terms / exceptions in both dictionaries

inter alia, inter alios, inter se, inter nos, inter vivos

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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intra

within

intraword, intra-aword

Examples

intraword: intraocular, intrapersonal, intrauterine, intravascular
intra-aword: intra-arterial *

* MW11 lists a few intra-awords.
WNW does not list any, but would hyphenate any unlisted terms by default rule.

Exceptions: None

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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macro

long, large

macroword

Examples: macroeconomics, macronutrient, macrophotography

Exceptions/odd: MW11 vs. WNW

Just one odd term listed in MW11 only.

MW11: macro lens

WNW: ———— (not listed but would probably agree)

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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mega

large, extremely

megaword

Examples: megadose, megahit, megawatt

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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micro

very small

microword
microoword for CMS / micro-oword for AP* except microorganism

Examples

microword: microbiology, microbrewery, microinjection

About microowords / micro-owords:

microorganism is the only microoword listed in each dictionary.

Based on the default rules:

CMS would prefer microoword.
AP would prefer micro-oword EXCEPT microorganism.

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional AP notes

AP specifically lists microsite, which is not in either dictionary.

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mid

in the middle of

midword, middword, mid-Cap
mid-number or mid-# using regular CMS and AP number rules (see below)

Examples

midword: midfield, midlife, midpoint, midsummer, midweek, midwinter, midyear
middword: midday

Exceptions/odd terms listed in both dictionaries

mid-ocean ridge, mid-rise (building), Midwest, Midwestern, Midwesterner

mid-Cap

While not listed in the dictionaries, mid-Cap words are common, especially with months.

mid-August
mid-Sunday

But note seasons are lowercased in both CMS and AP styles.
midsummer and midwinter are in both dictionaries.

With numbers

CMS: mid-number or mid-#
Spell out or use numerals using CMS rules.

mid-2017

mid-1990s (But if needed, the mid-nineties, or even more casual, the mid-’90s, would likely be the correct style but considered informal. These informal versions are not covered in CMS or Q&A, however.)

in his mid-forties

in the mid-twentieth century (as noun) or mid-twentieth-century design (as adjective).

CMS Q&A offers mid to late 1990s as an answer. So it would be his mid to late twenties. MW11 agrees—the MW11 app offers this format as a sentence example for mid.

AP: mid-#

mid-2017

mid-1990s (and more informally, the mid-’90s, but this is not covered by AP)

in his mid-40s

in the mid-20th century (as a noun) or mid-20th-century design (as adjective)

AP’s Ask the Editor offers these additional answers: mid-to-late 1990s, his mid-to-late 20s

Additional notes

AP’s Ask the Editor offers midcentury modern. CMS does not cover this one, but would likely agree with AP.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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mini

small

miniword

Examples: minicomputer, miniseries, minivan

Exceptions/odd: MW11 vs. WNW

All odd terms listed in both dictionaries.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

Minicam, mini-mart

WNW

minicam, ————

Additional notes

CMS also lists minimarket, which is not in either dictionary.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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mis

wrongly, unfavorably, opposite of

misword, mishword, missword

Examples

misword: miscommunication, misfortune, misrepresent
mishword: mishandle, mishap
missword: missaid, missent, misspend

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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multi

many, multiple

multiword, multi-iword

Examples

multiword: multicultural, multiethnic, multilingual
multi-iword: multi-industry, multi-instrumentalist *

MW11 lists some multi-iwords, but WNW does not. But by the default rule, WNW/AP would hyphenate them.

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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neo

new, recent

neoword
neooword for CMS & MW11 / neo-oword for AP & WNW
neo-Cap or Neo-Cap (varies, see table)

But many inconsistencies and odd terms. See table.

Examples

neoword: neoclassical, neonatal
neooword/neo-oword: neoorthodox (MW11) / neo-orthodox (WNW)
neo-Cap/Neo-Cap: see table

Exceptions/odd: Many. See table below.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Table below includes all exceptions and odd terms, plus a selection of normal ones. Gray, light blue, light pink: Not listed in this dictionary, so default rule applied.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP difference?
Usually neoword neooword neo-Cap or Neo-Cap If not in MW11 dictionary, apply same rules: neounlisted Exceptions and odd: white background	Usually neoword neo-oword neo-Cap or Neo-Cap If not in WNW dictionary, hyphenate: neo-unlisted. Exceptions and odd: white background	Agrees with WNW
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	blank = AP agrees w WNW / exception to normal rule or odd /
neoclassical	neoclassical
neocolonialism	neocolonialism
neoconservative	neoconservative
neo-Darwinism	Neo-Darwinism
neo-Expressionism	neo-Expressionism
neo-Freudian	neo-Freudian
Neogene	Neogene
neo-Gothic	neo-Gothic
neo-Hebraic	Neo-Hebraic
neo-impressionism	neoimpressionism
neo-Lamarckism	Neo-Lamarckism
Neo-Latin	Neo-Latin
neoliberal	neo-liberal (not listed, which makes it inconsistent with neoconservative, so ?)
neolith	neolith
neolithic	Neolithic
neo-Malthusian	neo-Malthusian
neonatal	neonatal
neo-Nazi, neo-Nazism	neo-Nazi, neo-Nazism
neoorthodox, neoorthodoxy	neo-orthodox, neo-orthodoxy
neo-pagan, neo-paganism	neopagan, neopaganism
neoplastic	neoplastic
neoplasticism	neoplasticism
Neoplatonism	Neoplatonism
neorealism	neorealism
neo-scholasticism	Neo-Scholasticism
neotropical	Neotropical

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non

not, of no importance

nonword, nonnword, non-Cap

Examples

nonword: nonaligned, nonbinding, nonfat, noninvasive, nonjudgmental, nonobjective, nonunion, nonviolence
nonnword / non-nword: nonnative, nonnecessity, nonnegotiable, nonnuclear but AP prefers non-nuclear*
non-Cap: non-American

MW11 lists several non-Cap words. WNW does not list any, but would hyphenate them by default.

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

nonbiblical, non-euclidean, non-Hodgkin’s lymphoma, non-Indo-European, non-insulin-dependent, nonjuror and nonjuring, non-oil BUT nonoily, nonpros/nonprossed/nonprossing, non-self-governing, ———, nonstarter, non-U

WNW

non-Biblical, non-Euclidean, non-Hodgkin’s lymphoma, non-Indo-European, ————————-, Nonjuror but nonjuring, —————-, non-pros/non-prossed/non-prossing, ——————-, non-sked, non-starter, non-U

*non-nuclear is an exception to WNW, but other nonnwords in dictionary do not need a hyphen.

Latin: non compos mentis, non placet, non obstante, non prosequitur, non sequitur
Italian: non troppo

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional notes

AP says “use a hyphen in awkward combinations.” Not certain how to interpret that. The only example they list is their one exception, non-nuclear. But their Q&A section says other nonnwords don’t have a hyphen per WNW.

The WNW app does not list many non words, but the actual WNW dictionary has a thorough list without definitions.

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over

excessive, surpassing

overword, overrword

Examples

overword: overact, overqualified, overseas
overrword: overreact, overrun

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

———-, over-ripeness BUT overripe, ————-

WNW

over-egg, ————– —————, over-under

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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para

beyond, outside of, or beside

paraword, para-aword

Examples

paraword: paralegal, paranormal, paraphrase, parasailing
para-aword: para-aminobenzoic acid

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

paradichlorobenzene

WNW

para-dichlorobenzene

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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post

after

postword
posttword for CMS / post-tword for AP*
post-Cap, post–Compound Cap

Examples

postword: postdoctoral, postmodern, postproduction, postwar
post-Cap: post-Christmas
post–Compound Cap:

post–Civil War (CMS uses en dash)
post-Civil War (AP uses hyphen)

*About posttwords / post-twords

*MW11 lists several posttwords, which are not hyphenated. posttax, posttest, posttreatment.
(But oddly, they prefer post-traumatic stress disorder, but posttraumatic on its own.)

WNW does not list any except post-traumatic, so by default rule, hyphenate. post-tax, post-test, post-treatment

Exceptions/odd: Many. See table below.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Table below includes all exceptions and odd terms, plus a selection of normal ones. Gray, light blue, light pink: Not listed in this dictionary, so default rule applied.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP difference?
Usually postword posttword post-Cap If not in MW11 dictionary, apply same rules: postunlisted	Usually postword posttword post-Cap If not in WNW dictionary, hyphenate: post-unlisted	Agrees with WNW with a few exceptions in orange.
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	AP agrees w WNW / AP disagrees w WNW / exception to normal rule or odd /
postbellum	post-bellum	post-bellum
post-communion	post-communion	post-communion
postconsumer	post-consumer	post-consumer
postconvention	post-convention	post-convention
postdate	postdate	postdate
postdoctoral	postdoctoral	postdoctoral
postelection	post-election	postelection
post-free	post-free	post-free
postgame	post-game	postgame
postgraduate	postgraduate	postgraduate
post-horse	post horse	post horse
post house	post house	post house
Postimpressionism	postimpressionism
Post-it (trademark)	Post-it (trademark)	Post-it (trademark)
post meridiem (alternate term not listed.)	post meridiem BUT postmeridian (both meaning p.m.)	post meridiem
postmortem	postmortem	post-mortem
postnuptial	postnuptial	postnuptial
(not listed, probably post obit?)	post-obit	post-obit
post obitum	post obitum	post obitum
post office	post office	post office
post-op	post-op	post-op
postoperative	postoperative	postoperative
post-polio syndrome	post-polio syndrome	post-polio syndrome
postrace	post-race	post-race
postracial	post-racial	post-racial
post road	post road	post road
postscript	postscript	postscript
post-structuralism	post-structuralism	post-structuralism
post time (horse racing)	post time (horse racing)	post time
posttraumatic (but post-traumatic stress disorder)	post-traumatic (based on entry for post-traumatic stress disorder)	post-traumatic
post-traumatic stress disorder (but note posttraumatic on its own)	post-traumatic stress disorder	post-traumatic stress disorder
post–World War II (with en dash)	post-World War II (with hyphen?)	post-World War II (with hyphen)
postwar	postwar	postwar

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pre

before

preword
preeword for CMS / pre-eword for AP (which disagrees with WNW)
pre-Cap, pre–Compound Cap

Examples

preword: postdoctoral, postmodern, postproduction, postwar

preeword:
preelection, preemptive, preestablish for CMS
but AP prefers pre-eword, so pre-election, pre-emptive, pre-establish

pre-Cap: pre-Christmas

pre–Compound Cap:

pre–Civil War (CMS uses en dash)
pre-Civil War (AP uses hyphen)

Exceptions/odd: Many. See table below.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Table below includes all exceptions and odd terms, plus a selection of normal ones. Gray, light blue, light pink: Not listed in this dictionary, so default rule applied.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP difference?
Usually preword preeword pre-Cap If not in MW11 dictionary, apply same rules: preunlisted	Usually preword preeword pre-Cap If not in WNW dictionary, hyphenate per AP: pre-unlisted	Agrees EXCEPT for pre-ewords. Hyphenate them.
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	blank = AP agrees w WNW / AP disagrees w WNW / exception to normal rule or odd /
preapprove	preapprove
prearrange	prearrange
Precambrian	Precambrian
precensor	pre-censor
pre-Christian	pre-Christian
pre-Columbian	pre-Columbian
precondition	precondition
preconvention	pre-convention	pre-convention (AP lists it as an example of “not in dictionary, so hyphenate.”)
precook	precook
predate	predate
predecease	predecease
predispose	predispose
preelection	preelection	pre-election
preeminent	preeminent	pre-eminent
preempt	preempt	pre-empt
pre-engineered	pre-engineered (not listed)	pre-engineered (agrees by default)
preestablish	preestablish	pre-establish
preexisting	preexisting	pre-existing
prefab	prefab
preflight	preflight
prefreshman	pre-freshman (not listed)
pregame	pre-game	pregame (specifically listed by AP)
preheat	preheat
pre-Hispanic	pre-Hispanic
prehistioric	prehistoric
preignition	preignition
prejudge	prejudge
pre-K	pre-k or pre-K
prekindergarten	prekindergarten
premarital	premarital
premarket	premarket
premed	pre-med
premedical	premedical
premoistened	pre-moistened
prenatal	prenatal
prenoon	pre-noon (not listed)	pre-noon (AP lists it as an example of “not in dictionary, so hyphenate.”)
prenuptial	prenuptial
pre-op	pre-op	According to AP Ask the Editor, it’s preop, “short for preoperative.” but since it’s not listed in AP Stylebook, WNW’s spelling of pre-op would likely be fine too.
preoperative	preoperative
pre-owned	pre-owned
prepay	prepay
prepackage	prepackage
prepossess	prepossess
preprint	pre-print (not listed)
Pre-Raphaelite	Pre-Raphaelite
prerecord	prerecord
preregister	preregister
presale	presale
preschool	preschool
preset	preset
preshrink	preshrink
presoak	pre-soak
pre-Socratic	pre-Socratic or Presocratic
presort	presort
pretax	pre-tax (not listed)	pretax (specifically listed in AP)
preteen	preteen
preteen-ager	not listed, so probably pre-teenager
preterm	preterm
pretest	pretest
prewar	prewar

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pro

supporting. substituting for. earlier than. in front of.

proword with exceptions for CMS, see table /
proword but pro-cause for AP (which disagrees with WNW)
pro-Cap, pro–Compound Cap

Examples

proword: proactive, probiotic, procreate

CMS: procause (probusiness, protax), except pro-life, pro-choice, etc. See table.
AP: pro-cause (pro-business, pro-tax), including pro-life, pro-choice, etc.

pro-Cap: pro-Christian

pro–Compound Cap:

pro–Civil War (CMS uses en dash)
pro-Civil War (AP uses hyphen)

Exceptions/odd: Many. See table below.

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Table below includes all exceptions and odd terms, plus a selection of normal ones. Gray, light blue, light pink: Not listed in this dictionary, so default rule applied.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP has different rules for pro!
Usually proword pro-Cap If not in MW11 dictionary, apply same rules: prounlisted	Usually proword pro-Cap If not in WNW dictionary, hyphenate per AP: pro-unlisted	Use pro-cause for support of a cause, but proword for others, and pro-Cap If not in WNW dictionary, hyphenate: pro-unlisted
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	AP agrees w WNW / AP disagrees w WNW / pro-cause / exception or odd /
proabortion	pro-abortion	pro-abortion
pro-abortionist	pro-abortionist	pro-abortionist
proactive	proactive	proactive
pro-am	pro-am	pro-am
probiotic	probiotic	probiotic
probusiness	pro-business	pro-business
pro-choice	pro-choice	pro-choice
pro-Clinton	pro-Clinton	pro-Clinton
procreate	procreate	procreate
pro-family	pro-family	pro-family
pro forma	pro forma	pro forma
proinsulin	proinsulin	proinsulin
prolabor	pro-labor	pro-labor
pro-life	pro-life	pro-life
promo	promo	promo
pronoun	pronoun	pronoun
propeace	pro-peace	pro-peace
prorate	prorate	prorate
pro shop	pro shop	pro shop
proslavery	proslavery	pro-slavery
pro-Trump	pro-Trump	pro-Trump
prowar	pro-war	pro-war
provitamin	provitamin	provitamin

Also consider Latin two-word terms: pro bono, pro forma, pro rata, pro tem, pro tempore.

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proto

first, original

protoword

Examples: protohistory, protoplanet, prototype

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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pseudo

not real, fake

pseudoword

Examples: pseudogene, pseudonym, pseudoscience

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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re

again

reword, rereword, re-cover vs. recover, etc.
reeword for CMS / re-eword for AP (which disagrees with WNW)

Examples

reword: react, regift, reinforce
reeword: reeducate, reenact for CMS / re-educate, re-enact for AP
rereword: reread, rerecord, rerelease
re-cover vs. recover, re-lay vs. relay, etc.

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

reembroidered, re-up

WNW

re-embroidered, re-up

use re-eword instead of reeword

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional notes

WNW’s app does not list most re- words, but its printed dictionary includes a thorough list without definitions.

All authorities agree that when re- means “again,” but the word conflicts with an existing word, use a hyphen to prevent ambiguity: re-ally, re-collect, re-cover, re-create, re-dress, re-form, re-lay, re-lease, re-present, re-press, re-sign, re-sort, re-trace, re-tread, etc.

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semi

partly, half

semiword, semi-iword

Examples

semiword: semiabstract, semifinalist, semiprivate
semi-iword: semi-independent, semi-invalid*

MW11 lists one semi-iword. WNW does not list any, but would hyphenate them by default rule.

*semi-invalid is not listed in either dictionary, but CMS lists it as an example of a semi-iword.

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

semi-antique, semiautomatic, semiautonomous, ——–

WNW

—————, semiautomatic*, semiautonomous*, semi-staged

*AP: two specific exceptions to WNW listed:

semi-automatic, semi-autonomous

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional notes

AP notes that semiannual and biannual both mean twice a year. (But biennial means every two years.)
Despite that fact, semimonthly means twice a month, but bimonthly means every other month.
Semiweekly means twice a week in MW11. But biweekly is listed in MW11 with two definitions: twice a week and every two weeks, and WNW says biweekly means every two weeks, but “now rare” usage considers it twice a week. WNW states semiweekly is the preferred term for twice a week. Arrgh! If you use this term, please make it clear exactly what you mean.

Table below includes all exceptions and odd terms, plus a selection of normal ones. Gray, light blue, light pink: Not listed in this dictionary, so default rule applied.

MW11 (CMS’s dictionary)	WNW (AP’s dictionary)	AP difference?
Usually semiword semi-iword semi-Cap If not in MW11 dictionary, apply same rules: semiunlisted	Usually semiword semi-iword semi-Cap If not in WNW dictionary, hyphenate per AP: semi-unlisted	Agrees with WNW, except semi-automatic and semi-autonomous
dictionaries agree / exception or odd / disagrees w WNW / not listed but disagrees w WNW / not listed but agrees w all /	dictionaries agree / exception or odd / disagrees w MW11 / not listed but disagrees w MW11 / not listed but agrees w all /	AP agrees w WNW / AP disagrees w WNW / exception to normal rule or odd /
semiabstract	semiabstract
semi-antique	semi-antique
semiannual	semiannual
semiarid	semiarid
semiautobiographical	semi-autobiographical
semiautomatic	semiautomatic	semi-automatic
semiautonomous	semiautonomous	semi-autonomous
semicircle	semicircle
semifinal	semifinal
semi-independent	semi-independent
semi-invalid (listed in CMS but not MW11)	semi-invalid
No other semi-iwords listed.	No semi-iwords listed at all.
semiofficial	semiofficial
semistaged	semi-staged
semitrailer	semitrailer
semitropical	semitropical

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socio

social, society

socioword

Examples: socioeconomic, sociopolitical, sociopath

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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sub

under

subword, subbword

Examples

subword: subfloor, subindex, suboptimal
subbword: subbase, subbasement, subbranch

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

subeditor, submachine gun

WNW

sub-editor, submachine gun

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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super

over, bigger, superior

superword
superrword for CMS / super-rword for AP

Examples: supercharge, superhero, supersensitive, superstructure

About superrwords / super-rwords

MW11 lists several superrwords, which are not hyphenated.
WNW does not list any, so for AP, hyphenate super-rwords by default rule.

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

Super Bowl, super-duper, ———–, superhigh frequency, ————————, ————-, ——————

WNW

Super Bowl, super-duper, Superfund, superhigh frequency, super middleweight, super PAC, Super Tuesday

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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supra

beyond, transcending, above

supraword, supra-Cap

Examples:

supraword: supramolecular, supranational, supraorbital
supra-Cap: supra-American

supra-Cap words are not listed in dictionaries but are hyphenated by default. CMS lists supra-American an example.

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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trans

across, change

transword, transsword, trans-Cap

Examples:

transword: transaction, transcontinental, transform, transgender, transnational
transsword: transship, transsonic
trans-Cap: trans-Siberian

trans-Cap words are not listed in dictionaries but are hyphenated by default. AP lists trans-Siberian as an example.

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

transatlantic, transpacific
trans fat, trans-fatty acid

WNW

transatlantic, transpacific
trans fat, —————–

AP lists two exceptions

trans-Atlantic, trans-Pacific
—————-, —————

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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tri

three

triword

Examples: triathlete, trioxide, trisyllable, triweekly

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

tristate

WNW

tri-state

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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ultra

extremely, more, beyond

ultraword

Examples: ultraconservative, ultraliberal, ultramodern, ultraviolet

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

ultra-pasteurized

WNW

——————–

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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un

not, opposite of

unword, un-Cap

Examples

unword: unabridged, uncertain, unchristian*, uninspired, unorganized, unusual
un-Cap: un-American

un-Cap words are not usually listed in dictionaries but are hyphenated by default.

*Both dictionaries prefer unchristian instead of un-Christian. MW11 lists the capitalized term as a secondary variant.

Exceptions/odd: MW11 vs. WNW

All exceptions listed in each dictionary.
Highlight: exception/odd. Blue/pink: disagreement. —–: not listed.

MW11

unair-conditioned
un-understandable
unselfconscious BUT self-conscious

CMS lists an exception: un-unionized, which is not in either dictionary.

WNW

unair-conditioned is not listed, but air-conditioned is, so it would likely be un-air-conditioned, but AP’s Ask the Editor suggest recasting the phrase.
un-understandable is not listed, so it would be hyphenated by the default rule.
unselfconscious BUT self-conscious

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional notes

WNW does not list most un words in its app, but its print dictionary includes a thorough list without definitions.

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under

beneath, below normal, subordinate

underword, underrword

Examples

underword: underachieve, underestimate, understaffed
underrword: underreact, underrepresent

Exceptions: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

Additional notes

underway / under way

MW11 has a notable preference that is losing ground in mainstream English:

under way: adverb (and predicate adjective). in progress, into motion, “Hunting season is well under way.” “Our trip got under way.”
underway: adjective, occurring while traveling in motion, “the underway bus ride.”

CMS does not mention underway / under way at all.

WNW only lists underway, adj., moving or making progress.

AP specifically says “underway: one word in all uses.”

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-war with prefix

prewar in both dictionaries

postwar in both dictionaries

prowar for CMS. This word is not listed in MW11 or CMS (including Q&A and forum), but this answer is derived from the default rules. It is consistent with antiwar and prewar.
pro-war in AP but not listed in WNW.

antiwar in MW11 for CMS
anti-war in AP, which is an exception from WNW, which lists antiwar with secondary variant anti-war

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.Sources:
CMS 16
AP 2017: see under hyphen, prefixes, and individual prefixes by term