Against is a preposition. When you do something against somebody or something, you oppose them or it.
- Human rights organizations have been campaigning against the death penalty.
- Are you against internet censorship?
When you play against somebody, you try to defeat them.
- Argentina lost the World Cup final match against Germany.
- We must fight against the anti-social elements that lead our kids astray.
If something counts against you, it causes you to have a disadvantage.
- She is 45, so her age may count against her.
If someone turns against you, they become unfriendly towards you.
- No one thought that he would turn against his own brother.
When you lean against a wall, you touch it.
If there is a law against something it is illegal.
- The country does have some legislation against child labor.
If you swim against the current, you move in the opposite direction.
- They were sailing against a strong wind.
- Why is there a preference for boys as against girls in many Asian countries?
Here is a list of idiomatic expressions using the word against.
Against the law
If something is against the law, it is not allowed by the law.
- It is against the law to smoke in public places.
Against your will
If you do something against your will, you do it, although you do not want to do it.
- Martha married her father’s friend against her will.
- No one should be forced to leave their home against their will.
Against someone’s wishes/advice
If someone does something against your wishes, they do it although you do not want them to do it.
- She married her boyfriend against her father’s wishes.