/ Dictionary / Index M M-radiation: Meaning and Definition of Find definitions for: M-ra•di•a•tion Pronunciation: (em'rā"dē-ā"shun), [key] — n. Physics. See under Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. MRA Mr. Big Related Content Daily Word Quiz: dissonant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language