Meaning of “against” - Learner’s Dictionary

against

preposition us uk /əˈɡenst/
Extra Examples
There are many arguments against nuclear energy.The massacre was a crime against humanity.They marched to London to protest against health cuts.He decided to speak out against the bombing.She was very active in the fight against drugs.
NOT AGREE

B2 disagreeing with a plan or activity:

Andrew wants to change offices but I'm against it.
There were 70 votes for the new proposal and 30 against.
COMPETE

A2 competing with or opposing someone or something:

Liverpool is playing against AC Milan.
the fight against racism
TOUCH

A2 touching something:

Push the bed against the wall.
PROTECT

protecting you from something bad:

Fresh fruit in the diet may protect against cancer.
OPPOSITE DIRECTION

B1 in the opposite direction to the way something is moving:

I was cycling against the wind.
against the law/the rules

B2 forbidden by a law or by rules:

It's against the law to leave young children alone in the house.
against sb's advice/wishes, etc

If you do something against someone's advice, wishes, etc, you do it although they have said you should not or must not:

He flew there against his doctor's advice.
have sth against sb/sth

to have a reason not to like someone or something:

I have nothing against him personally, I just don't think he's the right man for the job.

(Definition of “against” from the Cambridge Learner’s Dictionary © Cambridge University Press)