The Collaborative International Dictionary of English v.0.48:

Whoremaster \Whore"mas`ter\, n.
   1. A man who practices lewdness; a lecher; a whoremonger.
      [1913 Webster]

   2. One keeps or procures whores for others; a pimp; a
      procurer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

whoremaster
    n 1: a prostitute's customer [syn: whoremaster, whoremonger,
         john, trick]
    2: a pimp who procures whores [syn: whoremaster,
       whoremonger]