noun, plural id·i·o·syn·cra·sies.
- a characteristic, habit, mannerism, or the like, that is peculiar to an individual.
- the physical constitution peculiar to an individual.
- a peculiarity of the physical or the mental constitution, especially susceptibility toward drugs, food, etc.Compare allergy(def 1).
noun plural -sies
- a tendency, type of behaviour, mannerism, etc, of a specific person; quirk
- the composite physical or psychological make-up of a specific person
- an abnormal reaction of an individual to specific foods, drugs, or other agents
c.1600, from French idiosyncrasie, from 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” (see rare (adj.2)). Originally in English a medical term meaning “physical constitution of an individual.” Mental sense first attested 1660s.
n.
- A structural or behavioral trait peculiar to an individual or a group.
- A physiological or temperamental peculiarity.
- An unusual individual reaction to food or a drug.