Source : Webster's Revised Unabridged Dictionary (1913)

Idiopathic \Id`i*o*path"ic\, Idiopathical \Id`i*o*path"ic*al\,
   a. [Cf. F. idiopathique.] (Med.)
   Pertaining to idiopathy; characterizing a disease arising
   primarily, and not in consequence of some other disease or
   injury; -- opposed to {symptomatic}, {sympathetic}, and
   {traumatic}. -- {Id`i*o*path"ic*al*ly}, adv.

Source : WordNet®

idiopathic
     adj : (of diseases) arising from an unknown cause; "idiopathic
           epilepsy"