A prefix (affix) is a word, or letter(s) placed at the beginning of another word (a base word) to adjust or qualify its usage or meaning.
Understanding the meanings of the common prefixes can help us deduce the meanings of new words.

This table defines and illustrates the most common prefixes

Prefix Example

The opposite, a negative or reverse

in-  (in, into)

un-   (not/reverse action)

ab- (reverse action)

de- (reverse action)

non- (not)

dis-/di-/dif-  (apart)

im- (not/reverse action)

a- (not)

 

inaccurate

unavoidable

abdicate

decompound

dishonest

immature

nonexistent

atheist

Degree and quality

super- (above, over)

under-  (lower in grade/dignity)

sub-  (below, under)

semi-  (half)

hemi- (half) 

homo- (same)  

ultra- (beyond)

up- (higher, or better)

 

 

superficial

underestimate

suburban

semicircle

hemisphere

homogenous

ultrasonic

upgrade

Numbers and quantity

bi- (two)

uni- (one)

tri- (three)

twi- (two)

di- (two) 

du-/duo (two)

mono-, mon- (sole, only)

multi-, mult- (many)

omni- (all)

ambi- (both)  

 

 

bicycle

universal

tricycle

twilight

dioxide

duet

monosyllabic

multicultural

omnivore

ambivalent

Position, direction

trans- (over, through, across)

out- (better, faster, longer, farther)

back- (behind an object)

by- (near to)

down- (from higher/lesser)

fore-  (before, in front)

mid-  (middle) 

under- (below, beneath)

ex- (out of)

inter- (among, between)

intra- (inside, within)

 

transform

outcome

backporch

bypass

download

forearm

midstream

underwear

export

international

intravenous

Bad or wrong

mis- (wrong)

mal- (badly)

 

misfortune

malnourish

 

Attitude

pro-  (for, forward, in favour of)

anti-  (against, opposite)

counter- (against) 

with-  (against)

un- (against)

 

pro-life

anti-freeze

counterpart

withstand

unequal

Time

post- (after, behind)

neo- (new)

ex-  (out of)

pre-   (before)

 

post-graduation

neolithic

ex-husband

pre-election

With, along with, touching on

co- (joint, with, accompanying)

fellow-   (joint, with, accompanying)

con-/com-/col-/cor- (together or with) 

 

co-worker

fellow-worker

confederation

cohabit

correlation

 

Size

maxi- (very long, very large) 

mini-  (small)

midi- (medium-sized)

mega-, megalo- (great, large)

micro- (small)

 

 maxi-skirt

minivan

midi-length

megastar

micro-organism

The Meaning of English Suffixes