/ Dictionary / Index B black arm: Meaning and Definition of Find definitions for: black' arm" Pronunciation: [key] — Plant Pathol. Plant Pathol. a type or phase of bacterial blight of cotton, characterized by black, elongated lesions on the stem and branches, caused by a bacterium, Xanthomonas malvacearum. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Black Angus black art Related Content Daily Word Quiz: laudable Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language