/ Dictionary / Index M mass-energy equation: Meaning and Definition of Find definitions for: mass'-en'er•gy equa"tion Pronunciation: (mas'en'ur-jē), [key] — Physics. Physics. the equation, E=mc, formulated by Albert Einstein, expressing the equivalence between mass and energy, where E is energy, m is mass, and c is the velocity of light. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Massena Massenet 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