[buh-sil-uh s]

noun, plural ba·cil·li [buh-sil-ahy] /bəˈsɪl aɪ/.

any rod-shaped or cylindrical bacterium of the genus Bacillus, comprising spore-producing bacteria.
(formerly) any bacterium.

Origin of bacillus

1880–85; < Late Latin, variant of Latin bacillum (diminutive of baculum) staff, walking stick Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for bacillus

Contemporary Examples of bacillus

Historical Examples of bacillus

  • I shall see that your name is coupled with the Bacillus as that of its discoverer.

  • If you think my sorrow could have been avoided, offer the Bacillus as a wedding gift to—.

  • I found the story of the Bacillus, the curse that killed Darmstetter, that killed Helen.

  • The Bacillus is a cheat; every woman to her lover is the most beautiful!

  • They have succeeded in isolating the bacillus leprae and studying it.

British Dictionary definitions for bacillus


noun plural -cilli (-ˈsɪlaɪ)

any rod-shaped bacterium, such as a clostridium bacteriumCompare coccus (def. 2), spirillum (def. 1)
any of various rodlike spore-producing bacteria constituting the family Bacillaceae, esp of the genus Bacillus

Word Origin for bacillus

C19: from Latin: a small staff, from baculum walking stick
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for bacillus

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

Online Etymology Dictionary, © 2010 Douglas Harper

bacillus in Medicine



n. pl. ba•cil•li (-sĭlī′)

Any of various rod-shaped, usually gram-positive aerobic bacteria of the genus Bacillus that often occur in chains and include Bacillus anthracis, the causative agent of anthrax.
Any of various bacteria, especially a rod-shaped bacterium.



A genus of rod-shaped gram-positive bacteria capable of producing endospores.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

bacillus in Science



Plural bacilli (bə-sĭlī′)

Any of various pathogenic bacteria, especially one that is rod-shaped.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.