/ Dictionary / Index T tri-: Meaning and Definition of Find definitions for: tri- Pronunciation: [key] a combining form meaning “three,” used in the formation of compound words: triacid; triatomic. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. TRH triable Related Content Daily Word Quiz: frugal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language