The Collaborative International Dictionary of English v.0.48:

Hybridize \Hy"brid*i`ze\, v. t. [imp. & p. p. Hybridized; p.
   pr. & vb. n. Hybridizing.]
   To render hybrid; to produce by mixture of stocks.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hybridize \Hy"brid*ize\, v. i. (Biol.)
   To produce hybrid offspring; to interbreed; to cross.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

hybridize
    v 1: breed animals or plants using parents of different races
         and varieties; "cross a horse and a donkey"; "Mendel tried
         crossbreeding"; "these species do not interbreed" [syn:
         crossbreed, cross, hybridize, hybridise,
         interbreed]