A buttock is one of the two round, fleshy parts you sit on — the left or the right. Together they are the buttocks.

A buttockButtock（一邊臀部） is one of the two round, fleshy parts you sit on是你坐下時壓到的那兩塊圓圓肉肉的部位其中一個, the left or the right左邊或右邊. Together兩邊合起來 they are the buttocks就叫buttocks

In everyday talk people usually say bum, bottom, or behind; butt is the common informal American word for the same area. Buttock is the more anatomical word: a doctor, a biology book, or someone trying to be exact will use it. It is not a rude word by itself, but this part of the body still makes some students shy, so speakers often pick a softer everyday word unless they need to be precise.

In everyday talk people usually say bum, bottom, or behind平常說話大家通常會說bum、bottom或behind; butt is the common informal American word for the same areabutt則是美式口語裡常見的同一個部位說法. Buttock is the more anatomical wordButtock是比較解剖學的字: a doctor, a biology book, or someone trying to be exact will use it醫生、生物課本，或想講得精確的人會用它. It is not a rude word by itself這個字本身不算粗俗, but this part of the body still makes some students shy但這個身體部位還是會讓一些學生害羞, so speakers often pick a softer everyday word unless they need to be precise所以除非需要精確，說話的人常會挑比較委婉的日常用字

One person has two buttocks; one buttock is only one side.

One person has two buttocks一個人有兩個buttocks; one buttock is only one side一個buttock只是其中一邊

The word is old: from Middle English buttok, probably Old English buttuc, 'end; end piece,' and it has meant this part of the body since about 1300. It is probably a small-form of the older word behind butt, with the ending -ock.

The word is old這個字很古老: from Middle English buttok來自中古英文buttok, probably Old English buttuc, 'end; end piece,'可能來自古英文buttuc，意思是「末端；末端的一塊」 and it has meant this part of the body since about 1300從大約1300年起就是指身體這個部位. It is probably a small-form of the older word behind butt它大概是butt這個更老的字的「小稱形式」, with the ending -ock加上字尾-ock