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]

WordNet (r) 3.0 (2006):

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