buttock

例句：

1. 1.She sat down on a chair and crossed her legs.
   她坐在椅子上，交叉着腿。
2. 2. The woman was wearing a dress that hugged her buttock.
   这位女士穿着一条紧身裙，紧贴着她的臀部。
3. 3. He lifted his buttock to show off his muscles.
   他抬起臀部，炫耀他的肌肉。