- idiosyncrasy (n.)
- c. 1600, from French idiosyncrasie, from Latinized form of Greek idiosynkrasia "a peculiar temperament," from idios "one's own" (see idiom) + synkrasis "temperament, mixture of personal characteristics," from syn "together" (see syn-) + krasis "mixture," from PIE root *kere- "to mix, confuse; cook" (see rare (adj.2)).
Originally in English a medical term meaning "physical constitution of an individual;" mental sense "peculiar mixture" of the elements in one person that makes up his character and personality first attested 1660s. In modern use, loosely, one's whims, habits, fads, or tastes. Sometimes confused in spelling with words in -cracy, but it is from krasis not kratos.