/ Dictionary / Index B bacillus: Meaning and Definition of Find definitions for: ba•cil•lus Pronunciation: (bu-sil'us), [key] — pl. -cil•li any rod-shaped or cylindrical bacterium of the genus Bacillus, comprising spore-producing bacteria. See diag. under (formerly) any bacterium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: bacillus (Thesaurus) bacilluria bacillus Calmette-Guérin Related Content Daily Word Quiz: profiterole Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language