The Collaborative International Dictionary of English v.0.48:

Idiopathy \Id`i*op"a*thy\, n.; pl. Idiopathies. [Gr. ?;
   'i`dios proper, peculiar + ?, ?, to suffer: cf. F.
   idiopathie.]
   1. A peculiar, or individual, characteristic or affection.
      [1913 Webster]

            All men are so full of their own fancies and
            idiopathies, that they scarce have the civility to
            interchange any words with a stranger. --Dr. H.
                                                  More.
      [1913 Webster]

   2. (Med.) A morbid state or condition not preceded or
      occasioned by any other disease; a primary disease.
      [1913 Webster]

WordNet (r) 3.0 (2006):

idiopathy
    n 1: any disease arising from internal dysfunctions of unknown
         cause [syn: idiopathic disease, idiopathic disorder,
         idiopathy]