against的词性只有介词这一种，意思有反对；对…不利等。基本用法如下：

1、表示“反对”“对着”“违反”“不利于”等。如：

We are all against his idea. 我们都反对他的想法。

He was married against his will. 他结婚是有违本意的。

2、表示“靠着”“顶着”“迎着”“衬着”等。如：

He stood with his back against the door. 他背靠门站着。

He hit his head against the window. 他的头撞到了窗户上。

3、against是介词，所以后接动词时要用动名词。

I’m against doing anything till the police arrive. 我反对在警察到达之前采取任何行动。