Prefixes were originally words themselves but they are now groups of letters added to words or to roots to create new words. Prefixes [pre(before)+fix(fasten)=fasten before] are groups of letters placed before words or roots. Prefixes modify or extend the meaning of words and roots.
Source: http://www.southampton.liunet.edu/academic/pau/course/webpre.htm, modified by Rebecca Oberg
While it also discusses suffixes and root words, this catchy rap song gives great examples and some quick information about prefixes.
Source: YouTube
A prefix is a letter or a group of letters attached to the beginning of a word that partly indicates its meaning. For example, the word prefix itself begins with a prefix--pre-, which generally means "before."
Understanding the meanings of the common prefixes can help us deduce the meanings of new words that we encounter. But be careful: some prefixes (such as in-) have more than one meaning (in this example, "not" and "into").
The table below defines and illustrates 35 common prefixes.
| Prefix | Meaning | Example |
| a-, an- | without | amoral |
| ante- | before | antecedent |
| anti- | against | anticlimax |
| auto- | self | autopilot |
| circum- | around | circumvent |
| co- | with | copilot |
| com-, con- | with | companion, contact |
| contra- | against | contradict |
| de- | off, away from | devalue |
| dis- | not | disappear |
| en- | put into | enclose |
| ex- | out of, former | extract, ex-president |
| extra- | beyond, more than | extracurricular |
| hetero- | different | heterosexual |
| homo- | same | homonym |
| hyper- | over, more | hyperactive |
| il-, im-, in-, ir- | not, without | illegal, immoral, inconsiderate, irresponsible |
| in- | into | insert |
| inter- | between | intersect |
| intra- | between | intravenous |
| macro- | large | macroeconomics |
| micro- | small | microscope |
| mono- | one | monocle |
| non- | not, without | nonentity |
| omni- | all, every | omniscient |
| post- | after | postmortem |
| pre-, pro- | before, forward | precede, project |
| sub- | under | submarine |
| syn- | same time | synchronize |
| trans- | across | transmit |
| tri- | three | tricycle |
| un- | not | unfinished |
| uni- | one | unicorn |
