/ Dictionary / Index T trefoil arch: Meaning and Definition of Find definitions for: tre'foil arch" Pronunciation: [key] — Archit. Archit. an arch with cusplike intrados. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. trefoil trefoil knot 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