If something is dirty, it is marked or covered with stains, spots, or mud, and needs to be cleaned.

To dirty something means to cause it to become dirty.

If you describe an action as dirty, you disapprove of it and consider it unfair, immoral, or dishonest.

If you describe something such as a joke, a book, or someone's language as dirty, you mean that it refers to sex in a way that some people find offensive.

Dirty is used before words of criticism to emphasize that you do not approve of someone or something.

If you say that someone washes their dirty linen in public, you disapprove of their discussing or arguing about unpleasant or private things in front of other people. There are several other forms of this expression, for example wash your dirty laundry in public, or in American English, air your dirty laundry in public .

If someone gives you a dirty look, they look at you in a way which shows that they are angry with you.

Dirty old man is an expression some people use to describe an older man who they think shows an unnatural interest in sex.

To do someone's dirty work means to do a task for them that is dishonest or unpleasant and which they do not want to do themselves.

A dirty weekend is a weekend during which two people go away together, mainly in order to have sex.

If you say that an expression is a dirty word in a particular group of people, you mean it refers to an idea that they strongly dislike or disagree with.