手背的英文：
the back of hand

参考例句：

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

He took his arm from sonny's shoulder and slapped him, lightly, affectionately, with the back of his hand
他抽回搂着小弟弟肩膀的手臂，用手背亲热地轻轻拍了拍小弟。

back是什么意思：
n. 后面，背面，反面；背，背部；靠背；后卫
v. 支持；后退，倒退；背书；下赌注于
adj. 背部的；后面的；过去的；拖欠的.
adv. 以前；向后地；来回地；上溯

Stand back to back!
背靠背站好！

They are on the back of the menu.
它们在菜单背面。

Our seats on the train were back to back.
我们在火车上的坐位是背靠背的。

It happened far back in the past.
这事发生在久远的过去。

the back of a Chinese robe or jacket
后襟