pneumococcus

from WordNet (r) 3.0 (2006)

pneumococcus
    n 1: bacterium causing pneumonia in mice and humans [syn:
         {pneumococcus}, {Diplococcus pneumoniae}]

from The Collaborative International Dictionary of English v.0.48

Pneumococcus \Pneu`mo*coc"cus\, n. [See {Pneumo-}, and
   {Coccus}.] (Biol.)
   A form of micrococcus found in the sputum (and elsewhere) of
   persons suffering with pneumonia, and thought to be the cause
   of this disease.
   [1913 Webster]