Source : Webster's Revised Unabridged Dictionary (1913)

Idiosyncrasy \Id`i*o*syn"cra*sy\, n.; pl. {Idiosyncrasies}. [Gr.
   ?; ? proper, peculiar + ? a mixing together, fr. ? to mix
   together; ? with + ? to mix: cf. F. idiosyncrasie. See
   {Idiom}, and {Crasis}.]
   A peculiarity of physical or mental constitution or
   temperament; a characteristic belonging to, and
   distinguishing, an individual; characteristic susceptibility;
   idiocrasy; eccentricity.

         The individual mind . . . takes its tone from the
         idiosyncrasies of the body.              --I. Taylor.

Source : WordNet®

idiosyncrasy
     n : a behavioral attribute that is distinctive and peculiar to
         an individual [syn: {foible}, {mannerism}]