/ Dictionary / Index A acid-fast: Meaning and Definition of Find definitions for: ac•id-fast Pronunciation: (as'id fast", -fäst"), [key] — adj. resistant to decolorizing by acidified alcohol after staining. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: acid-fast (Thesaurus) acid dye acid-forming Related Content Daily Word Quiz: resilient Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language