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What Are Prefixes in English? Definition and Examples

Updated on December 8, 2022Grammar

Prefixes are one- to three-syllable affixes added to the beginning of a base word to slightly change its meaning. For example, adding the prefix im- to the base word possible creates a new word, impossible, which means “not possible.”

Prefixes are a regular part of English, and understanding them can greatly improve your vocabulary and reading comprehension. In this quick guide, we explain everything you need to know about prefixes and give plenty of examples of prefixes in English. But first, let’s talk a little about what prefix means. 

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What are prefixes?

Prefixes and suffixes are types of affixes, which are morphemes added to a base word to modify its meaning. Prefixes are added to the beginning of a word, while suffixes are added to the end. 

In English, the most common prefixes and suffixes are usually one or two syllables long, although some, like hetero- and megalo-, are three.

Prefixes always have the same meaning no matter what base word they’re attached to. For example, the prefix re- always means “to do something again”: when used in reread, it means “to read again”; when it’s used in rebuild, it means “to build again.” 

When to use prefixes

Prefixes are used mainly to shorten phrases into a single word. For example, instead of saying that someone is “achieving more than expected,” you can say simply that they’re “overachieving,” thanks to the prefix over-. In writing, prefixes are one of the best ways to streamline text and make it more potent. 

Prefixes are also important in academic disciplines, specifically to classify subjects. For example, biology is the study of living organisms, based on the prefix bio-, meaning “life,” but geology is the study of rocks and other earth minerals, based on the prefix geo-, meaning “relating to the earth.” 

Just be careful using prefixed words with a negative that you don’t create a double negative. Some prefixes, like a-, in-, or un-, are already negative. That means if you say “not unnecessary,” the two negatives cancel each other out, and the meaning is simply “necessary.” 

Prefixes and hyphens

From a grammar perspective, the most confusing part about using prefixes is when to use hyphens after them. Basically, some prefixed words use hyphens, and some don’t. To help you understand when to use hyphens with prefixes, here are some basic rules: 

Use a hyphen with the prefixes all-, ex– (former), and self

The prefixes all-, ex-, and self- use a hyphen. 

an all-knowing deity

my ex-partner

a self-aware creature

However, be careful with ex- because it has two different meanings—“out from,” and “in the past.” Use a hyphen only when the meaning of ex- is “former” or “in the past.” 

exterminator

ex-exterminator (a former exterminator) 

Also note that the prefix extra– is different from the prefix ex-, even though they start with the same two letters. The prefix extra- does not need a hyphen like the prefix ex-

extraterrestrial

Use a hyphen for prefixes with a proper noun

If you’re using a prefix with proper nouns, always use a hyphen.

a trans-Pacific flight

pro-Ukraine

The only exception is transatlantic, a unique word that does not follow the rules of proper nouns. 

Use a hyphen if adding the prefix spells a different word

Some words with prefixes, especially re-, are easily confused with other, preexisting words that happen to start with the same letters. If adding a prefix to a word creates a word that already exists, use a hyphen to clear up the ambiguity. 

After she recovers from the flu, the gardener needs to re-cover the flower beds. 

Use a hyphen to avoid putting the same vowels together

Most of the time, if the last letter of a prefix and the first letter of the base word are the same vowel, you use a hyphen. 

re-enter

semi-independent 

However, keep in mind this rule has exceptions. In particular, some prefixed words with pairs of o and e do not require a hyphen. 

cooperate

preexisting

When a prefix is added to a word that starts with a different vowel, you do not usually use a hyphen. 

reappraise

hydroelectric

Remembering which prefixed words use hyphens is confusing even for English experts. If you’re unsure, feel free to use a grammar checker.

Examples of prefixes in English

a-

not, without

amoral, atheist, asexual

after-

following something

afterlife, aftermath, aftereffect 

all-

including everything or completely

all-knowing, all-American, all-encompassing 

ambi-

both

ambidextrous, ambiguous, ambivalence

anti- 

against or opposing

anticlimactic, antibiotics, antiperspirant

astro-

relating to stars or outer space

astronomy, astrology, astronomical

auto-

by oneself

automobile, autobiography, automatic

back-

behind or reverse

backflip, background, backward

bi-

two

bicycle, bisexual, binary

bio-

life or relating to life

biology, biotechnology, biopsy

circum-

around

circumference, circumvent, circumstantial

co-, col-, com-, con-, cor-

together

co-pilot, colleague, correlation

contra-

against or opposing

contradiction, contraceptive, contrarian

counter-

opposition, often as a reaction

counterattack, counterbalance, counterpart

de-

down or away from

de-escalate, descend, devalue

dis-

negation or reversal

disapprove, dislike, dishonor

down-

moving from higher to lower

downgrade, download, downplay

ex-

former or in the past

ex-boyfriend, ex-wife, ex-president

ex-

out from 

expatriate, exclude, export

extra-

outside of

extradite, extraterrestrial, extracurricular

fore-

before or at the front

forecast, forefront, forearm

geo-

relating to the earth

geology, geography, geofence

hetero-

different 

heterosexual, heterogeneous, heteromorph

hind-

in the back or behind

hindsight, hindquarters, hinder

homo-

same

homosexual, homogeny, homophone

hydro-

relating to water

hydroelectric, hydrophobic, hydroplane

hyper-

excessive, above, or over

hyperactive, hyperbolic, hyperventilate

il-, im-, in-, ir-

negation or reversal

illegal, inanimate, irredeemable

in-

toward or within

include, insert, influence

inter-

among, between

international, internet, interact

intra-

on the inside, within

intramural, intravenous, intracellular

mal-

badly

malfunction, malnourished, malevolent

mega-, megalo-

very large

megalomaniac, megalodon, megafauna

micro-

very small

microscope, microaggression, microcosm

mid-

in the middle

midnight, midlife, midseason

mini-

small or less

minimum, minivan, miniature

mono-

one

monochrome, monogamous, monologue

multi-

more than one, many

multiple, multitask, multimillionaire

neo-

new iteration of something

neoclassical, neonatal, neoliberal

non-

not or negation

nonnegotiable, nonstop, nonsense

off-

not standard or away from

offbrand, offsides, offshore

omni-

encompassing all

omnipotent, omnibus, omnivore

on-

in the immediate vicinity

ongoing, onlooker, onset

out-

surpassing or going outside the normal

outperform, outmaneuver, outlier

over-

excessive or going above

overreact, overreach, overstep

pan-

including everything

pandemic, pansexual, panacea

para-

beside or beyond

parallel, paragraph, paranormal

peri-

around or about

perimeter, periscope, peripheral

photo-

relating to light

photography, photosynthesis, photon

poly-

many

polygon, polygamy, polytheism

post-

happening after

postpone, posthumously, postseason

pre-

happening before

prepare, predict, prefix

pro-

in support of

pro-union, pro-democracy, pro-form

pro-

moving forward or advancing

propulsion, progress, proceed

re-

doing something again

repeat, recycle, redo

self-

directed toward oneself

self-conscious, self-assured, self-checkout

semi-

partially, not completely

semiautonomous, semicircle, semiannual

sub-, sup-

below or from a lower position

submarine, suboptimal, subtropic

syn-, sym-

working together

synchronize, symmetry, syndicate

tele-

from a distance

telephone, television, telecommute

trans-

crossing or going beyond

transcontinental, transform, transgender

tri-

three

trident, triangle, triathlon 

un-

negation or the absence of

unimportant, unrest, uneventful

under-

beneath or insufficient

undercover, underwear, underestimate

uni-

one

uniform, unite, unicellular

up-

upward or higher

upgrade, upwind, update

with-

moving away from or resisting

withdrawal, withhold, withstand

Prefixes FAQs

What are prefixes?

Prefixes are short one- to three-syllable additions that are attached to the beginnings of words to slightly change their meaning. For example, adding the prefix tri- to the base word angle creates a new word, triangle, which means “a figure with three straight lines and three angles.”

How do prefixes work?

Prefixes generally mean the same thing no matter what word they belong to. For example, the prefixes syn- and -sym mean “to do something together”: When syn- is added to thesis, it makes synthesis, a “combination of ideas to form a theory or system.” When sym- is added to phony, it makes symphony, meaning “music intended for a full orchestra.”

When should you use prefixes? 

Prefixes help you use fewer words when communicating. For example, instead of saying that someone is “doing something over and over again,” you can say simply that they’re repeating, thanks to the prefix re-, which means “to do something again.”

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