Source : Webster's Revised Unabridged Dictionary (1913)

Heterogeneity \Het`er*o*ge*ne"i*ty\, n. [Cf. F.
   h['e]t['e]rog['e]n['e]it['e].]
   The state of being heterogeneous; contrariety.

         The difference, indeed the heterogeneity, of the two
         may be felt.                             --Coleridge.

Source : WordNet®

heterogeneity
     n : the quality of being diverse and not comparable in kind
         [syn: {heterogeneousness}] [ant: {homogeneity}]