The Collaborative International Dictionary of English v.0.48:

amnesia \am*ne"si*a\ ([a^]m*n[=e]"zh[u^] or
   [a^]m*n[=e]"z[i^]*[.a]), n. [NL., fr. Gr. 'amnhsi`a; 'a priv.
   + mna^sqai to remember.]
   1. (Med.) Forgetfulness; loss of long-term memory. --Quian.
      [1913 Webster + AS]

   2. (Med.) A defect of speech, from cerebral disease, in which
      the patient substitutes wrong words or names in the place
      of those he wishes to employ. [Obs.] --Quian.
      [1913 Webster + AS]

WordNet (r) 3.0 (2006):

amnesia
    n 1: partial or total loss of memory; "he has a total blackout
         for events of the evening" [syn: amnesia, memory loss,
         blackout]