The Collaborative International Dictionary of English v.0.48:

Unsex \Un*sex"\, v. t. [imp. & p. p. Unsexed; p. pr. & vb. n.
   Unsexing.] [1st pref. un- + sex.]
   To deprive of sex, or of qualities becoming to one's sex;
   esp., to make unfeminine in character, manners, duties, or
   the like; as, to unsex a woman.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unsex
    v 1: deprive of sex or sexual powers
    2: remove the qualities typical of one's sex; "She unsexed
       herself"
    3: make infertile; "in some countries, people with genetically
       transmissible disabilites are sterilized" [syn: sterilize,
       sterilise, desex, unsex, desexualize, desexualise,
       fix]