The Collaborative International Dictionary of English v.0.48:

Effeminize \Ef*fem"i*nize\, v. t.
   To make effeminate. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

effeminize
    v 1: to give a (more) feminine, effeminate, or womanly quality
         or appearance to; "This hairdo feminizes the man" [syn:
         feminize, feminise, effeminize, effeminise,
         womanize]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "effeminize":
   castrate, demasculinize, desex, desexualize, devitalize,
   effeminate, effeminatize, emasculate, enervate, etiolate, exhaust,
   geld, sissify, soften, sterilize, unman, unnerve, womanize