The Collaborative International Dictionary of English v.0.48:

Numbness \Numb"ness\, n.
   The condition of being numb; that state of a living body in
   which it loses, wholly or in part, the power of feeling or
   motion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

numbness
    n 1: partial or total lack of sensation in a part of the body; a
         symptom of nerve damage or dysfunction
    2: the trait of lacking enthusiasm for or interest in things
       generally [syn: apathy, indifference, numbness,
       spiritlessness]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "numbness":
   acedia, aloofness, analgesia, anesthesia, apathy, ataraxia,
   ataraxy, benumbedness, blah, blahs, callousness, comatoseness,
   deadness, detachment, disinterest, dispassion, dullness,
   electronarcosis, heartlessness, hebetude, hopelessness,
   impassibility, imperception, imperceptiveness, imperceptivity,
   impercipience, inappetence, inconsiderateness, indifference,
   insensibility, insensibleness, insensitiveness, insensitivity,
   insentience, insouciance, lack of appetite, languidness,
   lethargicalness, lethargy, listlessness, narcosis, narcotization,
   nonchalance, obtuseness, passiveness, passivity, phlegm,
   phlegmaticalness, phlegmaticness, pins and needles, plucklessness,
   resignation, resignedness, sloth, sluggishness, sopor,
   soporifousness, spiritlessness, spunklessness, stupefaction,
   stupor, supineness, thick skin, torpidity, torpidness, torpor,
   unconcern, unfeeling, unfeelingness, unperceptiveness,
   withdrawnness