Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

pneumococcus
     n : bacterium causing pneumonia in mice and humans [syn: {Diplococcus
         pneumoniae}]
     [also: {pneumococci} (pl)]