[ba.cil.lus] n, pl -li [NL, fr. ML, small staff, rod, dim. of L baculus staff, alter. of baculum] (ca. 1879) 1: any of a genus (Bacillus) of aerobic rod-shaped gram-positive bacteria producing endospores that do not thicken the rod and including many saprophytes and some parasites (as B. anthracis of anthrax); broadly: a straight rod-shaped bacterium
2: bacterium; esp: a disease-producing bacterium