Idiosyncrasy Definition

ĭdē-ō-sĭngkrə-sē

idiosyncrasies

noun

idiosyncrasies

The temperament or mental constitution peculiar to a person or group.

Webster's New World

Any personal peculiarity, mannerism, etc.

Webster's New World

An individual reaction to a drug, food, etc. that is different from the reaction of most people.

Webster's New World

Synonyms:

Other Word Forms of Idiosyncrasy

Singular:

idiosyncrasy

Plural:

First attested in 1604, in modern sense since 1665, from Old French idiosyncrasie, from Ancient Greek ἰδιοσυγκρασία (idiosunkrasia, “one’s own temperament”), from ἴδιος (idios, “one’s own”) + σύν (sun, “together”) + κρᾶσις (krasis, “temperament”).

From Wiktionary
Greek idiosunkrāsiā idio- idio- sunkrāsis mixture, temperament (sun- syn-) (krāsis a mixing kerə- in Indo-European roots)

From American Heritage Dictionary of the English Language, 5th Edition