quirk

Concise Oxford English Dictionary © 2008 Oxford University Press:
quirk/kwɜːk/

▶noun

• 1 a peculiar behavioural habit.

• 2 a strange chance occurrence.

• 3 a sudden twist, turn, or curve.

• 4 Architecture an acute hollow between convex or other mouldings.

▶verb move or be moved suddenly or jerkily.

– derivatives
quirkish adjective.

– origin C16 (as v.): of unknown origin.