From 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.