The Collaborative International Dictionary of English v.0.48:

Hybridization \Hy`brid*i*za"tion\, n.
   The act of hybridizing, or the state of being hybridized.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hybridization
    n 1: (genetics) the act of mixing different species or varieties
         of animals or plants and thus to produce hybrids [syn:
         hybridization, hybridisation, crossbreeding,
         crossing, cross, interbreeding, hybridizing]