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[bak-teer-ee-uh m] /bækˈtɪər i əm/
singular of bacteria.
Origin of bacterium
1840-50; < New Latin < Greek baktḗrion, diminutive of baktēría staff; akin to báktron stick, Latin baculum, bacillum


[bak-teer-ee-uh] /bækˈtɪər i ə/
plural noun, singular bacterium
[bak-teer-ee-uh m] /bækˈtɪər i əm/ (Show IPA)
ubiquitous one-celled organisms, spherical, spiral, or rod-shaped and appearing singly or in chains, comprising the Schizomycota, a phylum of the kingdom Monera (in some classification systems the plant class Schizomycetes), various species of which are involved in fermentation, putrefaction, infectious diseases, or nitrogen fixation.
1905-10; < New Latin < Greek baktḗria, plural of baktḗrion; see bacterium
Related forms
bacterial, adjective
bacterially, adverb
nonbacterial, adjective
nonbacterially, adverb
unbacterial, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for bacterium


the singular of bacteria


plural noun (sing) -rium (-rɪəm)
a very large group of microorganisms comprising one of the three domains of living organisms. They are prokaryotic, unicellular, and either free-living in soil or water or parasites of plants or animals See also prokaryote
Derived Forms
bacterial, adjective
bacterially, adverb
Word Origin
C19: plural of New Latin bacterium, from Greek baktērion, literally: a little stick, from baktron rod, staff
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for bacterium

c.1848, singular of bacteria (q.v.).



1847, plural of Modern Latin bacterium, from Greek bakterion "small staff," diminutive of baktron "stick, rod," from PIE *bak- "staff used for support." So called because the first ones observed were rod-shaped. Introduced as a scientific word 1838 by German naturalist Christian Gottfried Ehrenberg (1795-1876).

Online Etymology Dictionary, © 2010 Douglas Harper
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bacterium in Medicine

bacterium bac·te·ri·um (bāk-tēr'ē-əm)
n. pl. bac·te·ri·a (-tēr'ē-ə)
Any of the unicellular, prokaryotic microorganisms of the class Schizomycetes, which vary in terms of morphology, oxygen and nutritional requirements, and motility, and may be free-living, saprophytic, or pathogenic, the latter causing disease in plants or animals.

bacteria bac·te·ri·a (bāk-tǐr'ē-ə)
Plural of bacterium.

bac·te'ri·al adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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bacterium in Science
Plural bacteria
Any of a large group of one-celled organisms that lack a cell nucleus, reproduce by fission or by forming spores, and in some cases cause disease. They are the most abundant lifeforms on Earth, and are found in all living things and in all of the Earth's environments. Bacteria usually live off other organisms. Bacteria make up most of the kingdom of prokaryotes (Monera or Prokaryota), with one group (the archaea or archaebacteria) often classified as a separate kingdom. See also archaeon, prokaryote.

bacterial adjective
Our Living Language  : It is important to remember that bacteria is the plural of bacterium, and that saying a bacteria is incorrect. It is correct to say The soil sample contains millions of bacteria, and Tetanus is caused by a bacterium.

Plural of bacterium.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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bacterium in Culture

bacteria definition

sing. bacterium

Microorganisms made up of a single cell that has no distinct nucleus. Bacteria reproduce by fission or by forming spores.

Note: Some bacteria are beneficial to humans (for example, those that live in the stomach and aid digestion), and some are harmful (for example, those that cause disease).
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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