Source : Webster's Revised Unabridged Dictionary (1913)

Idiosyncratic \Id`i*o*syn*crat"ic\, Idiosyncratical
\Id`i*o*syn*crat"ic*al\, a.
   Of peculiar temper or disposition; belonging to one's
   peculiar and individual character.

Source : WordNet®

idiosyncratic
     adj : peculiar to the individual; "we all have our own
           idiosyncratic gestures"; "Michelangelo's highly
           idiosyncratic style of painting"