/ Dictionary / Index T trimester: Meaning and Definition of Find definitions for: tri•mes•ter Pronunciation: (trī-mes'tur, trī'mes-), [key] — n. a term or period of three months. one of the three approximately equal terms into which the year is divided by some colleges, schools, etc. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: trimester (Thesaurus) trimerous trimetallic Related Content Daily Word Quiz: profiterole Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language