Etymology
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bacteria (n.)

"unicellular microorganisms which lack an organized nucleus," and sometimes cause disease, 1847, plural of Modern Latin bacterium, from Greek bakterion "small staff," diminutive of baktron "stick, rod, staff, cudgel." So called because the first ones observed were rod-shaped. Introduced as a scientific word 1838 by German naturalist Christian Gottfried Ehrenberg. A classical plural sometimes also erroneously used as a singular.

The Greek word is from a PIE *bak- "staff used for support, peg" (compare Latin baculum "rod, walking stick;" Irish bacc, Welsh bach "hook, crooked staff;" Middle Dutch pegel "peg, pin, bolt"). De Vaan writes, "Since *b was very rare in PIE, and Celtic shows an unexplained geminate, we are probably dealing with a loanword from an unidentified source."

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bacterial (adj.)
"of or pertaining to bacteria," 1869, from bacteria + -al (1).
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bacteriology (n.)

"scientific study of microbes," 1884, from German; see bacteria + -ology. Related: Bacteriological (1886); bacteriologist. Bacteriological warfare is attested from 1924.

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archaebacteria (n.)

a name for microorganisms similar to bacteria but seemingly more primitive, 1977, from archaeo- "primitive, ancient" + bacteria. Singular is archaebacterium.

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eubacteria (n.)
singular eubacterium, 1939, coined in German 1930; see eu-, here meaning "good," + bacteria. Classically, as an adverb, eu should form compounds only with verbs.
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bacteriophage (n.)

"virus that parasitizes a bacterium by infecting it and reproducing inside it," 1921, from French bactériophage (1917), from bacterio-, combining form of bacteria, + -phage.

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bacillus (n.)

"rod-shaped bacterium," 1877, medical Latin, from Late Latin bacillus "wand," literally "little staff," diminutive of baculum "a stick, staff, walking stick," from PIE *bak- "staff" (also source of Greek bakterion; see bacteria) + instrumentive suffix -culo (see -cule). It was introduced as a term in bacteriology in 1853 by German botanist Ferdinand Cohn (1828-1898).

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anti-bacterial (adj.)

also antibacterial, 1875, from anti- + bacterial. Originally "opposed to the theory that

certain diseases are caused by bacteria;" later as "destructive to bacteria."  

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brucellosis (n.)
1930, Modern Latin, from Brucella, name of the bacteria that causes it, which is named for Scottish physician Sir David Bruce (1855-1931), who in 1887 discovered the bacteria, + -osis.
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