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[buh-sil-uh s] /bəˈsɪl əs/
noun, plural bacilli
[buh-sil-ahy] /bəˈsɪl aɪ/ (Show IPA)
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 Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for bacillus


noun (pl) -cilli (-ˈsɪlaɪ)
any rod-shaped bacterium, such as a clostridium bacterium Compare coccus (sense 2), spirillum (sense 1)
any of various rodlike spore-producing bacteria constituting the family Bacillaceae, esp of the genus Bacillus
Word Origin
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
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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
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bacillus in Medicine

bacillus ba·cil·lus (bə-sĭl'əs)
n. pl. ba·cil·li (-sĭl'ī')

  1. 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.

  2. Any of various bacteria, especially a rod-shaped bacterium.

Bacillus (bə-sĭl'əs)
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.
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bacillus in Science
Plural bacilli (bə-sĭl'ī')
Any of various pathogenic bacteria, especially one that is rod-shaped.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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