The Collaborative International Dictionary of English v.0.48:

Numb \Numb\, v. t. [imp. & p. p. Numbed (n[u^]md); p. pr. &
   vb. n. Numbing (n[u^]m"[i^]ng).]
   To make numb; to deprive of the power of sensation or motion;
   to render senseless or inert; to deaden; to benumb; to
   stupefy.
   [1913 Webster]

         For lazy winter numbs the laboring hand. --Dryden.
   [1913 Webster]

         Like dull narcotics, numbing pain.       --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

desensitizing \desensitizing\ adj.
   making less susceptible or sensitive to either physical or
   emotional stimuli. Opposite of sensitizing. [Narrower
   terms: numbing]
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

numbing
    adj 1: causing numbness or insensitivity; "the numbing effect of
           grief"