buttock

詳細解釋：

but.tock

n.（名詞）

Either of the two rounded prominences on the human torso that are posterior to the hips and formed by the gluteal muscles and underlying structures.
半邊屁股，臀部：人的軀體上位於臀部的由臀肌和下層組織構成的兩個圓形突起的任何一個
The analogous part of the body on certain mammals.
屁股：某種哺乳動物身體上功能相似的部分
buttocks The rear pelvic area of the human body.
buttocks 臀部：人體上接近骨盆的部位

來源：
Middle English
中古英文
from Old English buttuc [strip of land, end] * see bhau-
源自 古英文 buttuc [帶狀土地，末尾] *參見 bhau-