From The Collaborative International Dictionary of English v.0.44 [gcide]:
Microorganism \Mi'cro*["o]r"gan*ism\, noun [Micro- + organism.] (Biol.) Any microscopic form of life; a form of life too small to be seen by the naked eye; -- particularly applied to bacteria, protozoa, yeasts, and similar organisms, esp. such are supposed to cause infectious diseases.
From WordNet (r) 2.0 [wn]:
From Moby Thesaurus II by Grady Ward, 1.0 [moby-thes]:
100 Moby Thesaurus words for "microorganism": Euglena, adenovirus, aerobe, aerobic bacteria, aerobic organism, amoeba, anaerobe, anaerobic bacteria, anaerobic organism, animalcule, autotrophic organism, bacillus, bacteria, bacterium, being, bug, coccus, colon bacillus, creature, crumb, diatom, disease-producing microorganism, dot, drop, droplet, dyad, echovirus, enterovirus, filterable virus, flagellate, fleck, flyspeck, fungus, genetic individual, germ, gnat, grain, gram-negative bacteria, gram-positive bacteria, heterotrophic organism, individual, iota, jot, living being, living thing, microbe, microspore, microzoa, midge, minim, minutia, minutiae, mite, mold, monad, morphological individual, mote, nematode, nonfilterable virus, ont, organic being, organism, organization, paramecium, particle, pathogen, physiological individual, picornavirus, pinhead, pinpoint, point, protozoa, protozoon, reovirus, rhinovirus, rickettsia, salmonella, saprophyte, scrap, snip, snippet, speck, spirillum, spirochete, spore, sporozoon, staphylococcus, streptococcus, tetrad, tittle, triad, trypanosome, vanishing point, vibrio, virus, volvox, vorticellum, zooid, zoon, zoospore
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