/ Dictionary / Index P phenytoin: Meaning and Definition of Find definitions for: phen•y•to•in Pronunciation: (fen"i-tō'in, fu-nit'ō-), [key] — n. Pharm. a barbiturate-related substance, CHNO, used as an anticonvulsant in the treatment of grand mal epilepsy and in focal seizures. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: phenytoin (Thesaurus) phenyl valerate pheochromocytoma Related Content Daily Word Quiz: fervor Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language