The Collaborative International Dictionary of English v.0.48:

desensitize \desensitize\ v. t.
   to rendered insensitive or less sensitive. Opposite of
   sensitize.

   Syn: deaden.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

desensitize
    v 1: cause not to be sensitive; "The war desensitized many
         soldiers"; "The photographic plate was desensitized" [syn:
         desensitize, desensitise] [ant: sensitise,
         sensitize]
    2: make insensitive; "His military training desensitized him"
       [syn: desensitize, desensitise] [ant: sensibilise,
       sensibilize, sensify, sensitise, sensitize]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "desensitize":
   KO, anesthetize, bedaze, benumb, besot, blunt, chloroform,
   coldcock, deaden, dope, drug, dull, etherize, freeze, hebetate,
   kayo, knock out, knock senseless, knock stiff, knock unconscious,
   lay out, mull, narcotize, numb, obtund, palsy, paralyze,
   put to sleep, stun, stupefy