The Collaborative International Dictionary of English v.0.48:

Feminization \Fem`i*ni*za"tion\, n.
   The act of feminizing, or the state of being feminized.
   [1913 Webster]

WordNet (r) 3.0 (2006):

feminization
    n 1: the process of becoming feminized; the development of
         female characteristics (loss of facial hair or breast
         enlargement) in a male because of hormonal disorders or
         castration [syn: feminization, feminisation]