/ Dictionary / Index T triennium: Meaning and Definition of Find definitions for: tri•en•ni•um Pronunciation: (trī-en'ē-um), [key] — pl. -en•ni•ums, -en•ni•a a period of three years. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. triennial triens 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