idiosyncrasy /ˌɪdiə(ʊ)ˈsɪŋkrəsi 
/ ▸ noun (plural idiosyncrasies)
1 a mode of behaviour or way of thought peculiar to an individual: one of his little idiosyncrasies was always preferring to be in the car first.
▪ a distinctive or peculiar feature or characteristic of a place or thing: the idiosyncrasies of the prison system.
2 Medicine an abnormal physical reaction by an individual to a food or drug. – ORIGIN early 17th century (originally in the sense ‘physical constitution peculiar to an individual’): from Greek idiosunkrasia, from idios ‘own, private’ + sun ‘with’ + krasis ‘mixture’.
EnglishOxford Dictionary of English