Source : Webster's Revised Unabridged Dictionary (1913)

Epilepsy \Ep"i*lep`sy\, n. [L. epilepsia, Gr. ? a seizure, the
   ``falling sickness,'' fr. ? to take besides, seize, attack;
   'epi` upon, besides + ? to take: cf. F. ['e]pilepsie. Cf.
   {Catalepsy}.] (Med.)
   The ``falling sickness,'' so called because the patient falls
   suddenly to the ground; a disease characterized by paroxysms
   (or fits) occurring at interval and attended by sudden loss
   of consciousness, and convulsive motions of the muscles.
   --Dunglison.

Source : WordNet®

epilepsy
     n : a disorder of the central nervous system characterized by
         loss of consciousness and convulsions