bacillus (n.)

1877, medical Latin, from Late Latin bacillus "wand," literally "little staff," diminutive of baculum "a stick, staff, walking stick," from PIE *bak- "staff" (also source of Greek bakterion; see bacteria) + instrumentive suffix -culo. Introduced as a term in bacteriology 1853 by German botanist Ferdinand Cohn (1828-1898).