A prefix is a letter or a group of letters/word fixed to the beginning of a word that affects the meaning of the root word. A clue to knowing the meaning of new words is knowing what the prefix means. Being able to recognize prefixes is essential to building your vocabulary.
Here are some of the most used prefixes.
| PREFIX | DEFINITION | EXAMPLES | COMMENTS |
| a-, an- | not, lack of, without | asymptomatic, anacidic, | a- before consonants, an- before vowels |
| acro- | high | acrophobia, acro-yoga, | |
| ante- | before, earlier, prior, in front of | antecedent, anterior | |
| anti- | against, opposite of | anticlimax, antivaccine | |
| auto- | self, same | autopilot, autofocus | |
| be- | to be made | behead, bediamond, befall | |
| bi- | Twice, in two | biannual, biangular | |
| co- | together, with | cohabit, coadapt. | |
| com-, con- | together, with | comingle, contact | |
| contra-, contro- | against, opposite | contraindication, contrast, controversy, | |
| circum- | about, around | circumvent, circumcise | |
| de- | away from, down, off | detach, demotivate | |
| dis- | apart, away, not | disengage, disarm, disappear | |
| en- ex- extra- | put into, cover with former, out of, from beyond, outside, more than | engulf, enrage, extract, extraordinary | |
| hetero- | different, other | heterosexual, heterocyclic | |
| homo-, homeo- | same, alike | homonid, homeostatis | |
| hyper- | beyond, more, over | hyperactive, hyperventilate | |
| il-, im-, in-, ir- | without, not | Illicit, impossible, infertile, irresponsible | |
| in- im- | in, into | Influx, imbibe | |
| inter-, | between, among | interact, interject | |
| intra-, intro- | within, inside | intra-country, intravenous | |
| macro- | prominent, large | microorganism, macrocracked | |
| micro- | very small, minute | microfilament, micromanage | |
| mono- | one, single, alone | monogram, monotonous | |
| non- | not, without | non-issue, nonentity | |
| omni- | all, every | omnipresent, omnivore | |
| post- | after, behind | postnatal, postmodern | |
| pre-, pro- | before, forward | prebirth, proclaim | |
| sub- | lower, under | subordinate, subsaturate | |
| sym-, syn | same time, together | symbiotic, synergy | |
| tele- | over or from a distance | telepathy, telegraphic | |
| trans- | beyond, across, through | transactional, transact | |
| tri- | every third, three | trinomial, tricycle | |
| un- | lacking, not, opposite of | unrepentant, uninteresting | |
| uni- | single, one | unilateral, unilingual | |
| up- | higher/better, northwards, to the top | upstage, upend, uptitling | |
| ultra- | greater, beyond, outside of, excessive, | ultrasecret, ultrasonic, ultramicroscopic |
