The Collaborative International Dictionary of English v.0.48:

amnesiac \amnesiac\ adj. ([a^]m*n[=e]"z[-e]*[a^]k)
   Having lost memories, especially due to brain injury or
   mental shock; suffering from amnesia.

   Syn: amnesic
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

amnesiac \am*ne"si*ac\ ([a^]m*n[=e]"z[-e]*[a^]k), n. (Med.)
   A patient suffering from amnesia.
   [AS]

WordNet (r) 3.0 (2006):

amnesiac
    adj 1: suffering from a partial loss of memory [syn: amnesic,
           amnesiac]
    n 1: a person suffering from amnesia [syn: amnesic,
         amnesiac]