The Collaborative International Dictionary of English v.0.48:

Whoremonger \Whore"mon`ger\, n.
   A whoremaster; a lecher; a man who frequents the society of
   whores.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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