idiosyncrasy (n.) Look up idiosyncrasy at
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 first attested 1660s.