ba·​cil·​lus | \ bə-ˈsi-ləs How to pronounce bacillus (audio) \
plural bacilli\ bə-​ˈsi-​ˌlī How to pronounce bacillus (audio) also  -​lē \

Definition of bacillus

1 : any of a genus (Bacillus) of rod-shaped gram-positive usually aerobic bacteria producing endospores and including many saprophytes and some parasites (such as B. anthracis of anthrax) broadly : a straight rod-shaped bacterium
2 : bacterium especially : a disease-producing bacterium

Examples of bacillus in a Sentence

Recent Examples on the Web The ReencleMicrobe mix at the heart of this process contains rice husks, vermiculite, nonpathogenic bacillus bacteria, ammonium sulfate, and wood pellets, according to the company. Richard Baguley, Wired, 31 Mar. 2022 Scientists postulate that the bacillus originated in some lower animal and jumped to humans. Washington Post, 23 Mar. 2022 The technique is a deadly bacteria bacillus, one that first emerges in one corner of the world and is spreading far and wide, with consequences that could prove disastrous for hundreds of millions of people. Frida Ghitis, CNN, 14 Sep. 2021 Now nearly two dozen clinical trials around the world are underway to determine whether the bacillus Calmette-Guérin (BCG) vaccine against tuberculosis could protect against COVID-19. Melinda Wenner Moyer, Scientific American, 27 Oct. 2020 Once the bacillus and its antibacterial medication were discovered, the TB patient was no longer exiled but treated within, and assimilated by, the same socioeconomic framework as the rest of us. Joseph Osmundson, The New Republic, 30 July 2020 The masses of poor religious Jews in Poland were almost accidental to the effort; the real target was the élite, who brought with them the bacillus of cosmopolitanism. Adam Gopnik, The New Yorker, 15 June 2020 Most doctors assumed the disease was caused by a bacterium; the recently discovered Pfeiffer’s bacillus (Haemophilus influenzae), which was sometimes present in pathology specimens, was the prime suspect. Wendy Moore, Time, 28 Apr. 2020 Also, the early use of face masks which predated Wu's discovery of the bacillus as pneumonic. Paul French, CNN, 18 Apr. 2020 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'bacillus.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of bacillus

1868, in the meaning defined at sense 1

History and Etymology for bacillus

New Latin, from Medieval Latin, small staff, rod, diminutive of Latin baculus staff, alteration of baculum

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The first known use of bacillus was in 1868

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Last Updated

13 Apr 2022

Cite this Entry

“Bacillus.” Dictionary, Merriam-Webster, Accessed 16 May. 2022.

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More Definitions for bacillus


ba·​cil·​lus | \ bə-ˈsil-əs How to pronounce bacillus (audio) \
plural bacilli\ -​ˌī also -​ē \

Medical Definition of bacillus

1a capitalized : a genus of rod-shaped gram-positive endospore-producing usually aerobic bacteria of the family Bacillaceae that include many saprophytes and some parasites (as B. anthracis of anthrax)
b : any bacterium of the genus Bacillus broadly : a straight rod-shaped bacterium
2 : bacterium especially : a disease-producing bacterium

More from Merriam-Webster on bacillus

Nglish: Translation of bacillus for Spanish Speakers

Britannica English: Translation of bacillus for Arabic Speakers Encyclopedia article about bacillus


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