bun 
/ˈbʌn/ noun
plural buns /ˈbʌn/ noun 1 [count] : a small, round or long bread for one person to eat
▪ tuna salad served on a bun [=roll] ▪ a hamburger/hotdog bun 2 [count] : a small, usually round sweet cake
▪ cinnamon buns — see also sticky bun 3 [count] : a way of arranging long hair by twisting it into a round shape at the sides or back of the head
▪ She wears her hair in a bun. 4 buns [plural] US, informal : the two soft parts of the body that you sit on : buttocks
▪ This exercise will firm up your buns.
▪ tuna salad served on a bun [=roll] ▪ a hamburger/hotdog bun
▪ cinnamon buns — see also sticky bun
▪ She wears her hair in a bun.
▪ This exercise will firm up your buns.
have a bun in the oven
informal : to be pregnant
▪ Rumor has it, she has a bun in the oven.
▪ Rumor has it, she has a bun in the oven.
