/ Dictionary / Index M magnesium peroxide: Meaning and Definition of Find definitions for: magne'sium perox'ide Pronunciation: [key] a white, tasteless, water-insoluble powder, MgO, used as an antiseptic and as an oxidizing and bleaching agent. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. magnesium oxide magnesium silicate Related Content Daily Word Quiz: gregarious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language