The Collaborative International Dictionary of English v.0.48:

Dispersion \Dis*per"sion\, n. [CF. F. dispersion.]
   1. The act or process of scattering or dispersing, or the
      state of being scattered or separated; as, the Jews in
      their dispersion retained their rites and ceremonies; a
      great dispersion of the human family took place at the
      building of Babel.
      [1913 Webster]

            The days of your slaughter and of your dispersions
            are accomplished.                     --Jer. xxv.
                                                  34.
      [1913 Webster]

   2. (Opt.) The separation of light into its different colored
      rays, arising from their different refrangibilities.
      [1913 Webster]

   Dispersion of the optic axes (Crystallog.), the separation
      of the optic axes in biaxial crystals, due to the fact
      that the axial angle has different values for the
      different colors of the spectrum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dispersion
    n 1: spreading widely or driving off [syn: dispersion,
         scattering]
    2: the spatial or geographic property of being scattered about
       over a range, area, or volume; "worldwide in distribution";
       "the distribution of nerve fibers"; "in complementary
       distribution" [syn: distribution, dispersion] [ant:
       compactness, concentration, denseness, density,
       tightness]
    3: the act of dispersing or diffusing something; "the dispersion
       of the troops"; "the diffusion of knowledge" [syn:
       dispersion, dispersal, dissemination, diffusion]