The Collaborative International Dictionary of English v.0.48:

Miscegenation \Mis`ce*ge*na"tion\, n. [L. miscere to mix + the
   root of genus race.]
   A mixing of races; amalgamation, as by intermarriage of black
   and white.

   Note: Until the late twentieth century, misceganation was a
         crime in some states of the Southern United States.
         [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

miscegenation
    n 1: reproduction by parents of different races (especially by
         white and non-white persons) [syn: miscegenation,
         crossbreeding, interbreeding]