/ Dictionary / Index M magnesia: Meaning and Definition of Find definitions for: mag•ne•sia Pronunciation: (mag-nē'zhu, -shu), [key] — n. a white, tasteless substance, magnesium oxide, MgO, used in medicine as an antacid and laxative. Cf. Mag•ne•si•a Pronunciation: (mag-nē'shē-u, -zhē-u), [key] — n. ancient name of Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: magnesia (Thesaurus) magnate magnesite Related Content Daily Word Quiz: panacea Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language