/ Dictionary / Index L law of mass action: Meaning and Definition of Find definitions for: law' of mass' ac'tion Pronunciation: [key] — Chem. Chem. the statement that the rate of a chemical reaction is proportional to the concentrations of the reacting substances. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. law of Malus Law of Moses Related Content Daily Word Quiz: acerbity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language