屁股的一半的英文：
buttock

The back section of the buttock on the outside may be sensitive to the touch.
这块肌肉在臀部后面外侧的部分，可以很容易就摸到。

He buttocked his opponent onto the mat.
他把对手背摔在垫子上。

Armor consisting of overlapping plates used to protect the buttocks
护臀甲由相互交迭的甲片构成的铠甲，用来保护臀部

To expose one's buttocks in public as a prank or disrespectful gesture.
露出屁股以戏弄在公共场合暴露自己的屁股，作为一种恶作剧或不尊重的表示

All at once he became conscious of a smart blow upon his buttocks
突然之间，他觉得他的屁股上很疼地挨了一下打。