/ Dictionary / Index T trimethadione: Meaning and Definition of Find definitions for: tri•meth•a•di•one Pronunciation: (trī-meth"u-dī'ōn), [key] — n. Pharm. a synthetic, white, crystalline powder, CHNO, used as an anticonvulsant to control petit mal epileptic seizures. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. trimeter trimethoprim Related Content Daily Word Quiz: vertigo Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language