The Collaborative International Dictionary of English v.0.48:

Peacemaker \Peace"mak`er\, n.
   One who makes peace by reconciling parties that are at
   variance. --Matt. v. 9.
   [1913 Webster] --Peace"mak`ing, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

peacemaker
    n 1: someone who tries to bring peace [syn: conciliator,
         make-peace, pacifier, peacemaker, reconciler]
    2: a belt-fed machine gun capable of firing more than 500 rounds
       per minute; used by United States troops in World War II and
       the Korean War [syn: Browning machine gun, Peacemaker]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "peacemaker":
   adjudicator, alleviative, alleviator, anodyne, appeaser,
   arbitrator, assuager, balm, calmative, conchie, conciliator,
   conscientious objector, cushion, diplomat, dolorifuge, dove,
   family counselor, go-between, interceder, intermediary,
   intermediator, lenitive, make-peace, marriage counselor, mediator,
   mitigator, moderator, modulator, mollifier, negotiator,
   pacificator, pacificist, pacifier, pacifist, palliative,
   peace lover, peacekeeper, peacemonger, peacenik, placater,
   propitiator, reconciler, referee, restraining hand, salve,
   sedative, shock absorber, smoother-over, soother, soothing syrup,
   stabilizer, temperer, tranquilizer, umpire, wiser head