The Collaborative International Dictionary of English v.0.48:

Prodrome \Pro"drome\, n. [Gr. ? running before; ? before + ? to
   run: cf. F. prodrome.]
   1. A forerunner; a precursor.
      [1913 Webster]

   2. (Med.) A premonitory symptom; a symptom or sensation
      experienced by a person which presages the onset of a
      disease or abnormal physiological event; as, the prodrome
      of an epileptic seizure.
      [PJC]

WordNet (r) 3.0 (2006):

prodrome
    n 1: an early symptom that a disease is developing or that an
         attack is about to occur [syn: prodrome, prodroma]