/ Dictionary / Index M mustard gas: Meaning and Definition of Find definitions for: mus'tard gas" Pronunciation: [key] an oily liquid, CHClS, used as a chemical-warfare gas, blistering the skin and damaging the lungs, often causing blindness and death: introduced by the Germans in World War I. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mustard family mustard oil Related Content Daily Word Quiz: winsome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language