The Collaborative International Dictionary of English v.0.48:

analgesia \an`al*ge"si*a\ ([a^]n`[a^]l*j[=e]"z[-e]*[.a]), n.
   [NL., fr. Gr. 'analghsi`a; 'an priv. + a`lghsis sense of
   pain.] (Med.)
   Absence of sensibility to pain. --Quain. AS
   [1913 Webster]

WordNet (r) 3.0 (2006):

analgesia
    n 1: absence of the sense of pain without loss of consciousness

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "analgesia":
   abatement, allayment, alleviation, anesthesia, anesthetizing,
   anxiety equivalent, appeasement, assuagement, callousness,
   deadening, deadness, depraved appetite, diminishment, diminution,
   dulling, dullness, ease, easement, easing, electronarcosis,
   impassibility, imperception, imperceptiveness, imperceptivity,
   impercipience, inconsiderateness, insensibility, insensibleness,
   insensitiveness, insensitivity, insentience, lessening, lulling,
   mitigation, mollification, narcosis, narcotization, neurasthenia,
   numbing, numbness, obtuseness, palliation, paresthesia, parorexia,
   pica, pins and needles, reduction, relief, remedy, salving,
   softening, soothing, speech abnormality, subduement, thick skin,
   unfeeling, unfeelingness, unperceptiveness