Glossary
prefix
A prefix is the part fixed to the front of a word, and its job is to point that word in a direction rather than to name its subject.
A prefix is the part fixed to the front of a word, and its whole job is to point the word in a direction. The prefix never carries the subject of the term; it modifies whatever the rest of the word names. The part brady- slows the thing it is attached to, while tachy- speeds the same thing up. The part pre- places what follows earlier in time and post- places it later; anti- sets the word against something and a- takes it away. Learning the prefixes as directions rather than as vocabulary means one small part answers for a great many terms. A reader who knows that inter- means between can read an unfamiliar term without having met it before. Some terms open with more than one prefix, and each one keeps its own job.
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Related terms
Source: The word-part meanings in the MedlinePlus Understanding Medical Words tutorial (U.S. National Library of Medicine, a U.S. government work in the public domain), restated in our own words for the vocabulary guide in this exam, which prints the acknowledgement Courtesy of MedlinePlus from the National Library of Medicine. (MedlinePlus tutorial accessed 2026-10-07; definition written 2026-10-13)