prep.反对；逆；违背；倚靠；映衬；防御；相比；相对

There are 26 votes for him and 8 against him. 有26票赞成他，8票反对他。

We sailed against the wind. 我们逆风航行。

It's against your promise to go on smoking. 继续抽烟,这违背了你的诺言。

They forced me to do things against my will. 他们强迫我做违背我心意的事。

He propped himself against the wall. 他倚靠着墙。

We have saved some money against our old age. 我们存了一些钱，以备老年之用。

Our defences must be reinforced against attack. 我们必须加强防御设施以抵御进攻。

His eloquence did not avail against the facts. 他的雄辩在事实面前不起什么作用。

You must weigh the benefits against the cost. 你一定要权衡利益与成本二者的得失。

against用在fight，strive，struggle等词后面，同with意思相同，不过against更强调一种困难中的反抗。 We fight for the weak against the strong.

作为介词，against后接的宾语有时可省略。 He had intended to come but somehow decided against(it).

against作“反对”解时反义词是for。