The Collaborative International Dictionary of English v.0.48:

Warmonger \War"mon`ger\, n.
   One who makes ar a trade or business; a mercenary. [R.]
   --Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

warmonger
    n 1: a person who advocates war or warlike policies [syn:
         militarist, warmonger]