Source : Webster's Revised Unabridged Dictionary (1913)

Micrococcus \Mi`cro*coc"cus\, n.; pl. {Micrococci}. [NL. See
   {Micro-}, and {Coccus}.] (Biol.)
   A genus of {Spherobacteria}, in the form of very small
   globular or oval cells, forming, by transverse division,
   filaments, or chains of cells, or in some cases single
   organisms shaped like dumb-bells ({Diplococcus}), all without
   the power of motion. See Illust. of {Ascoccus}.

   Note: Physiologically, micrococci are divided into three
         groups; chromogenic, characterized by their power of
         forming pigment; zymogenic, including those associated
         with definite chemical processes; and pathogenic, those
         connected with disease.

Diplococcus \Dip`lo*coc"cus\, n.; pl. {Diplococci}. [NL., fr.
   Gr. ? twofold + ? grain, seed.] (Biol.)
   A form of micrococcus in which cocci are united in a binary
   manner. See {Micrococcus}.

Source : WordNet®

diplococcus
     n : gram-positive bacteria usually occurring in pairs
     [also: {diplococci} (pl)]