The Collaborative International Dictionary of English v.0.48:

Panacea \Pan`a*ce"a\, n. [L., fr. Gr. pana`keia fr. panakh`s
   all-healing; pa^s pa^n, all + 'akei^sqai to heal.]
   [1913 Webster]
   1. A remedy for all diseases; a universal medicine; a
      cure-all; catholicon; hence, a relief or solace for
      affliction.
      [1913 Webster]

   2. (Bot.) The herb allheal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Panacea
    n 1: (Greek mythology) the goddess of healing; daughter of
         Aesculapius and sister of Hygeia
    2: hypothetical remedy for all ills or diseases; once sought by
       the alchemists [syn: panacea, nostrum, catholicon,
       cure-all]