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[buh-sil-uh s]
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noun, plural ba·cil·li [buh-sil-ahy] /bəˈsɪl aɪ/.
  1. any rod-shaped or cylindrical bacterium of the genus Bacillus, comprising spore-producing bacteria.
  2. (formerly) any bacterium.
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Origin of bacillus

1880–85; < Late Latin, variant of Latin bacillum (diminutive of baculum) staff, walking stick
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for bacilli


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

Word Origin and History for bacilli


plural of bacillus (q.v.).

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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).

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Online Etymology Dictionary, © 2010 Douglas Harper

bacilli in Medicine


n. pl. ba•cil•li (-sĭlī′)
  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.
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  1. A genus of rod-shaped gram-positive bacteria capable of producing endospores.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

bacilli in Science


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

bacilli in Culture



sing. bacillus

One of three forms of bacteria, usually rod-shaped.

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The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.