I caught him by the arm.是什么意思？

I caught him by the arm.

我抓住他的胳膊。

caught

v. 赶上( catch的过去式和过去分词 )，接住，引起，看见；

例句
The men were caught in the act of digging up buried explosives.
那些人在挖掘掩埋的爆炸物时被逮个正着。

him

pron. (he的宾格)他；

例句
They said goodbye to him as he got aboard the train at Union Station.
当他在联合火车站登上火车之际，他们向他道别。

by

prep. 在…旁边，表示方式，由于，经过；adv. 经过，表示保留或保存时用，短暂拜访；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

arm

n. 臂，武器，[复数]战事，权力；vi. 准备（斗争），准备行动（against）；vt. 装备（防御工事），准备（攻击或迎击），配备，防护；

例句
He has never put an arm around his wife to accommodate photographers...
他从未为了迎合摄影师而搂住妻子。