Webster's English Dictionary

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bacterium

bac.te.ri.um \bak-'tir-e--*m\ \-e--*\ n or bac.te.ria [NL, fr. Gk 
   bakte-rion staff; skin to L baculum staff] pl  : any of a class 
   (Schizomycetes) of microscopic plants having round, rodli ke, spiral, or 
   filamentous single-celled or noncellular bodies often aggregated into 
   colonies or motile by means of flagella, living in soil, water, organic 
   matter, or the bodies of plants and animals, and being autotrophic, 
   saprophytic, or parasitic in nutrition and important to man because of 
   their chemical effects and as pathogens