WordNet (r) 3.0 (2006):

anaerobe
    n 1: an organism (especially a bacterium) that does not require
         air or free oxygen to live

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "anaerobe":
   adenovirus, aerobe, aerobic bacteria, amoeba, anaerobic bacteria,
   bacillus, bacteria, bacterium, bug, coccus,
   disease-producing microorganism, echovirus, enterovirus,
   filterable virus, fungus, germ, gram-negative bacteria,
   gram-positive bacteria, microbe, microorganism, mold,
   nonfilterable virus, pathogen, picornavirus, protozoa, protozoon,
   reovirus, rhinovirus, rickettsia, spirillum, spirochete, spore,
   staphylococcus, streptococcus, trypanosome, vibrio, virus