The Collaborative International Dictionary of English v.0.48:

Catholicon \Ca*thol"i*con\, n. [Gr. ?, neut. ?, universal. See
   Catholic.] (Med.)
   A remedy for all diseases; a panacea.
   [1913 Webster]

WordNet (r) 3.0 (2006):

catholicon
    n 1: hypothetical remedy for all ills or diseases; once sought
         by the alchemists [syn: panacea, nostrum, catholicon,
         cure-all]