The Collaborative International Dictionary of English v.0.48:

butch \butch\ (b[.u]ch), adj.
   1. markedly masculine in appearance or manner; -- used of
      men.

   Syn: macho.
        [WordNet 1.5]

   2. same as lesbian. [pejorative]
      [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

butch \butch\ n.
   a lesbian who is noticeably masculine.

   Syn: dyke.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

butch
    adj 1: used of men; markedly masculine in appearance or manner
           [syn: butch, macho]
    2: (of male or female homosexuals) characterized by
       stereotypically male traits or appearance
    n 1: (slang) offensive term for a lesbian who is noticeably
         masculine [syn: butch, dike, dyke]