The Collaborative International Dictionary of English v.0.48:

Coccus \Coc"cus\, n.; pl. Cocci. [NL., fr. Gr. ? grain, seed.
   See Cochineal.]
   1. (Bot.) One of the separable carpels of a dry fruit.
      [1913 Webster]

   2. (Zool.) A genus of hemipterous insects, including scale
      insects, and the cochineal insect (Coccus cacti).
      [1913 Webster]

   3. (Biol.) A form of bacteria, shaped like a globule.
      [1913 Webster]

WordNet (r) 3.0 (2006):

coccus
    n 1: any spherical or nearly spherical bacteria [syn: coccus,
         cocci]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "coccus":
   adenovirus, aerobe, aerobic bacteria, amoeba, anaerobe,
   anaerobic bacteria, bacillus, bacteria, bacterium, bug,
   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