/ Dictionary / Index P protoxide: Meaning and Definition of Find definitions for: pro•tox•ide Pronunciation: (prō-tok'sīd, -sid), [key] — n. Chem. the one of a series of oxides having the smallest proportion of oxygen. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. prototype protoxylem Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language