The Collaborative International Dictionary of English v.0.48:

Disarm \Dis*arm"\, v. t. [imp. & p. p. Disarming; p. pr. & vb.
   n. Disarming.] [OE. desarmen, F. d['e]sarmer; pref. d['e]s-
   (L. dis-) + armer to arm. See Arm.]
   1. To deprive of arms; to take away the weapons of; to
      deprive of the means of attack or defense; to render
      defenseless.
      [1913 Webster]

            Security disarms the best-appointed army. --Fuller.
      [1913 Webster]

            The proud was half disarmed of pride. --Tennyson.
      [1913 Webster]

   2. To deprive of the means or the disposition to harm; to
      render harmless or innocuous; as, to disarm a man's wrath.
      [1913 Webster]

WordNet (r) 3.0 (2006):

disarm
    v 1: remove offensive capability from [syn: disarm,
         demilitarize, demilitarise] [ant: arm, build up,
         fortify, gird]
    2: make less hostile; win over; "Her charm disarmed the
       prosecution lawyer completely"
    3: take away the weapons from; render harmless [syn: disarm,
       unarm]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "disarm":
   allure, appease, attract, bewitch, captivate, charm, conciliate,
   cripple, deactivate, decommission, deflate, demilitarize,
   demobilize, disable, disband, enchain, enchant, fascinate, gag,
   hamstring, handcuff, hobble, hog-tie, immobilize, incapacitate,
   knock out, manacle, mollify, muzzle, pacify, paralyze, placate,
   propitiate, prostrate, put at ease, reconcile, reconvert,
   set at ease, sheathe the sword, silence, strangle, throttle,
   truss up, win over