The Collaborative International Dictionary of English v.0.48:

Microcosm \Mi"cro*cosm\, n. [F. microcosme, L. microcosmus, fr.
   Gr. mikro`s small + ko`smos the world.]
   1. A little world; a miniature universe. Hence (so called by
      Paracelsus), a man, as a supposed epitome of the exterior
      universe or great world. Opposed to macrocosm. --Shak.
      [1913 Webster]

   2. A relatively small object or system considered as
      representative of a larger system of which it is part,
      exhibiting many features of the complete system.
      [PJC] Microcosmic

WordNet (r) 3.0 (2006):

microcosm
    n 1: a miniature model of something