Common Prefixes and their Meanings

A prefix is a meaningful unit of letters attached to the beginning of a word

Adding a prefix to a word changes the meaning or grammatical role of the original word.

The following is a list of some common prefixes, their meanings, and examples of the prefix attached to a word.

Anti- : against: antifreeze / antilock / antibacterial

Ab- / Abs- : away, from, separated: absent / abhor / abstract

Ambi- / Amphi- : both, around, combining from: amphitheater / amphibian / ambivalent / ambidextrous

Co- / Com- / Con- : with, together: connect / contain / comply

De- : down from, reverse, remove, out of, derived from: descend / decide

Di- / Dif- / Dis- : separation, negation, apart, in different directions: discharge / dismember / dislike

In- / Im- / Il- / Ir- : not: injustice / impossible / irresponsible / illegal

Mis- : wrongly / not: misunderstand / misfire / misgivings

Non- / Un- : not: nonsense / nonsmoker / unkind / unravel

Pre- : before, in front of: pretest / preview / prewriting

Pro- : in favor of or advancing: proponent / propel / progress

Re- / Retro-: backwards, back, again: retrograde / review / revision

Semi- : half of: semiannual / semicircle

Sub- : under, up from under, secondary action: submarine / subvert / subsequent / sublet

Syl- / Sym- / Syn- : united, together with, same as: synchronize / symbol / symmetry

Tra- / Trans- : beyond, across, through, on or to the other side: transgress / transatlantic / transcending 

Some prefixes are very similar to one another, and can sometimes cause confusion when you are trying to use prefixes to determine the meaning or definition of a word. Here are four groups of look-a-like prefixes:

1. Group One: the outsiders
   1. The prefixes ec-/ecto-/ex- all mean outside of, external, or away from.
   2. The prefix ex- can also mean out, from, or completely. Think of the word explain—which means to make things plain and clear—if we break it down, we can see how the prefix helps create its meaning: ex (completely) + plain = to make things completely plain (and clear).
   3. The prefix extra- looks like it would belong with the others, but it actually expresses a sense of being outside of something by going beyond it. Extraordinary means to be outside and beyond the ordinary.
       
2. Group Two: too much or too little
   1. The prefix hyper- means more, beyond the normal amount, excessive: hyperthermia: when the body temperature is way above normal
   2. The prefix hypo- means less, under, or below: hypothermia: when the body temperature is way below normal
       
3. Group Three: you’re either in or not
   1. The prefixes in-/im-/em-/en- all mean in, on, amongst, or within
      1. For example: ensnare = en- (within) + snare = within a snare (trap)
   2. The prefixes in-/im- can also both mean not
      1. For example: That email was very impersonal = im- (not) + personal = not personal
          
4. Group Four: Infra- / Intra- / Inter-
   1. The prefix infra- means below or beneath: infrared
   2. The prefix intra- means within or on the inside: intramural sports
   3. The prefix inter- means between or among: international (between nations)