/ Dictionary / Index B black mustard: Meaning and Definition of Find definitions for: black' mus'tard. Pronunciation: [key] See under(def. 2). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Black Muslim black nationalism Related Content Daily Word Quiz: mamba Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language