IDIOSYNCRASY, a physical or mental condition peculiar to an individual, usually taking the form of a special suscepti bility to particular stimuli ; thus it is an idiosyncrasy of one in dividual that abnormal sensations of discomfort should be ex cited by certain odours or colours, by the presence in the room of a cat, etc. ; similarly, certain persons are found to be peculiarly responsive or irresponsive to the action of particular drugs. The word is also used, generally, of any eccentricity or peculiarity of character, appearance, etc.