/ Dictionary / Index M MMT: Meaning and Definition of Find definitions for: MMT Pronunciation: [key] See methylcyclopentadienyl manganese tricarbonyl, CHMnO, a lead-free, toxic antiknock gasoline additive. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. M.M.Sc. M.Mus. Related Content Daily Word Quiz: longevity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language