The Collaborative International Dictionary of English v.0.48:

anaesthesia \an`[ae]s*the"si*a\, anesthesia
\an`es*the"si*a\([a^]n`[e^]s*th[=e]"z[-e]*[.a] or
   [a^]n`[e^]s*th[=e]"zh[.a]), n. [NL., fr. Gr. 'anaisqhsi`a;
   'an priv. + a'i`sqhsis feeling, a'isqa`nesqai to feel: cf. F.
   anesth['e]sie. See aesthetics.] (Med.)
   Entire or partial loss or absence of feeling or sensation; a
   state of general or local insensibility produced by disease
   or by the inhalation or application of an anaesthetic. AS
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Anesthesia \An`es*the"si*a\, n., Anesthetic \An`es*thet"ic\, a.
   Same as An[ae]sthesia, An[ae]sthetic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

anesthesia
    n 1: loss of bodily sensation with or without loss of
         consciousness [syn: anesthesia, anaesthesia]

Moby Thesaurus II by Grady Ward, 1.0:

100 Moby Thesaurus words for "anesthesia":
   abatement, allayment, alleviation, analgesia, anesthetizing,
   anxiety equivalent, appeasement, assuagement, autism, callousness,
   catatonia, chill, chilliness, cold blood, cold heart,
   coldheartedness, coldness, coolness, deadening, deadness, deadpan,
   depraved appetite, diminishment, diminution, dispassion,
   dispassionateness, dulling, dullness, ease, easement, easing,
   electronarcosis, emotional deadness, emotionlessness, frigidity,
   frostiness, heartlessness, iciness, immovability, impassibility,
   impassiveness, impassivity, imperception, imperceptiveness,
   imperceptivity, impercipience, inconsiderateness, inexcitability,
   insensibility, insensibleness, insensitiveness, insensitivity,
   insentience, lack of affect, lack of feeling, lack of touch,
   lessening, lulling, mitigation, mollification, narcosis,
   narcotization, neurasthenia, numbing, numbness, objectivity,
   obtuseness, palliation, paresthesia, parorexia, passionlessness,
   pica, pins and needles, poker face, reduction, relief, remedy,
   salving, self-absorption, softening, soothing, soullessness,
   speech abnormality, spiritlessness, straight face, subduement,
   thick skin, unemotionalism, unexcitability, unfeeling,
   unfeelingness, unimpressibility, unimpressionableness,
   unpassionateness, unperceptiveness, unresponsiveness,
   unsusceptibility, unsympatheticness, untouchability, withdrawal