idiosyncrasy

[id-ee-uh-sing-kruh-see, -sin-] [ˌɪdiəˈsɪŋkrəsi, -ˈsɪn-]
noun
  • quirk; a peculiar behavior or habit
  • "The [letters] are part of a single set belonging to a certain idiosyncratic hostess who was known for her lavish entertaining and scandalous hedonism."