Glossary
prefix
A prefix is the part fixed to the front of a medical word, and it changes direction, size, speed, number or negation without changing what the word is about.
A prefix is the part fixed to the front of a medical word, and it changes direction, size, speed, number or negation without changing what the word is about. Brady- means slow and tachy- means fast, so bradycardia and tachycardia name the same heart with opposite rates; hypo- and hyper- are a pair in the same way, and reading one as the other reverses the meaning. A prefix is attached to the root and is not used alone. A few pairs are spelled almost alike — ante- (before) against anti- (against), inter- (between) against intra- (within) — so the last letters decide the word. Some words carry no prefix at all: a term can be root plus suffix, and assuming a piece that is not there is how gastritis gets read as though a prefix were present. Read the prefix to its final letter, then the root, then the suffix, and only then put the meaning into a sentence.
Taught in
Related terms
- root — The root is the part of a medical word that says what the word is about — the organ, the tissue or the substance — and everything else in the word modifies it.
- context clue — A context clue is information in the sentence around an unknown word that narrows what the word means — a definition, a restatement, a contrast, an example, a consequence or the general sense.
- combining vowel — A combining vowel — almost always o — is the vowel placed between a root and a suffix when the suffix starts with a consonant.
- word part — A word part is a prefix, root, suffix or combining vowel — one of the pieces a medical word is built from.
- position prefix — A position prefix says where something is — pre- before, post- after, sub- under, supra- above, peri- around, inter- between.
Source: MedlinePlus (US National Library of Medicine) consumer guidance on understanding medical words, which the vocabulary guide follows for the prefix, root, suffix and combining-vowel system. US federal government material, not subject to copyright in the United States. Every definition and example above was written for this course in our own words; no dictionary or glossary text is reproduced. (MedlinePlus accessed 2026-10-27; definitions written 2026-10-27)