1911 Encyclopædia Britannica/Idiosyncrasy

IDIOSYNCRASY (Gr. ἰδιοσυγκρασία, peculiar habit of body or temperament; ἴδιος, one’s own, and σύγκρασις, blending, tempering, from συγκεράννυσθαι, to put together, compound, mix), a physical or mental condition peculiar to an individual usually taking the form of a special susceptibility to particular stimuli; thus it is an idiosyncrasy of one individual that abnormal sensations of discomfort should be excited by certain odours or colours, by the presence in the room of a cat, &c.; 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, &c.