The Collaborative International Dictionary of English v.0.48:

Caduceus \Ca*du"ce*us\, n. [L. caduceum, caduceus; akin to Gr. ?
   a herald's wand, fr. ? herald.] (Myth.)
   The official staff or wand of Hermes or Mercury, the
   messenger of the gods. It was originally said to be a
   herald's staff of olive wood, but was afterwards fabled to
   have two serpents coiled about it, and two wings at the top.
   [1913 Webster]

WordNet (r) 3.0 (2006):

caduceus
    n 1: an insignia used by the medical profession; modeled after
         the staff of Hermes