Glossary
prefix
A prefix is a word part added to the front of a root that changes its meaning — un-, re-, pre-, sub- and trans- among them. Learning a few unlocks dozens of words.
A prefix is a word part fixed to the front of a root to change its meaning. re- turns do into redo, un- turns certain into uncertain, and trans- turns port (carry) into transport (carry across). Because a prefix does not change the root's part of speech, it is the cheapest way to widen a vocabulary you already have: learn the part, and every word built on it opens.
The high-frequency set is small. Not: un-, dis-, in-, and its forms im-, il- and ir-. Again or back: re-. Before and after: pre-, post-. Position: sub- (under), trans- (across), inter- (between), super- (above). Direction of feeling: anti- (against), bene- and mal- (good and bad), mis- (wrongly).
Two cautions. A prefix may carry more than one sense — in- alone means both not and into — so check the word against the sentence rather than the spelling. And letters that look like a prefix may not be doing that job at all: the under in understand is not working the way under works in underground.
Taught in
Related terms
- suffix — A suffix is a word part added to the end of a root. It can change the meaning and, unlike a prefix, it usually changes the word's part of speech.
- word root — A word root is the part of a word carrying its core meaning, with prefixes and suffixes built onto it. Most English roots come from Latin or Greek, and one root usually builds a whole family.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)