Prefixes: One word or hyphenated?

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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

extraword

numberfold

geoword

hydroword

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.

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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.

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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.

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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.

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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.

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bio

life, of living things

bioword

Examples: biochemistry, bioethics, biohazard

Exceptions/odd: none

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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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
i
f 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

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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.

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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.

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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.

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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.

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-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.

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hydro

water, liquid, or containing hydrogen

hydroword

Examples: hydroelectric, hydroplane, hydrospace

Exceptions: None

If not in dictionary

CMS: Follow same pattern.
AP: Hyphenate.

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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.

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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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meta

transcending, more comprehensive (as in the study of a study). located behind or outside of. changing.

metaword, meta-aword

Examples:

metaword: metadata, metaethics, metaphysical
meta-aword: meta-analysis

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

AP

*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:

postCivil 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

AP

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