/ Dictionary / Index R radium A: Meaning and Definition of Find definitions for: radium A Pronunciation: [key] — Chem. Chem. a substance, formed by decay of radon, that gives rise to radium B. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. radium radium B 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