/ Dictionary / Index M Mr. Big: Meaning and Definition of Find definitions for: Mr. Big Pronunciation: [key] a man having the highest authority, control, prestige, or influence in a group, field, situation, or the like, esp. in the underworld. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. M-radiation MRBM 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