/ Dictionary / Index T triduum: Meaning and Definition of Find definitions for: trid•u•um Pronunciation: (trij'-um, trid'y-), [key] — n. Rom. Cath. Ch. a series of special religious observances over a three-day period, in preparation for a great feast. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. tridimensional tridymite Related Content Daily Word Quiz: dissonant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language