bun

Concise Oxford English Dictionary © 2008 Oxford University Press:
bun/bʌn/

▶noun

• 1 a small cake or bread roll.

• 2 a woman's hairstyle in which the hair is drawn into a tight coil at the back of the head.

• 3 (buns) N. Amer. informal a person's buttocks.

– phrases
have a bun in the oven informal be pregnant.

– origin ME: of unknown origin.