When you act, you do something for a particular purpose.

If you act on advice or information, you do what has been advised or suggested.

If someone acts in a particular way, they behave in that way.

If someone or something acts as a particular thing, they have that role or function.

If someone acts in a particular way, they pretend to be something that they are not.

When professionals such as lawyers act for you, or act on your behalf, they are employed by you to deal with a particular matter.

If a force or substance acts on someone or something, it has a certain effect on them.

If you act, or act a part in a play or film, you have a part in it.

An act is a single thing that someone does.

If you say that someone's behaviour is an act, you mean that it does not express their real feelings.

An Act is a law passed by the government.

An act in a play, opera, or ballet is one of the main parts into which it is divided.

An act in a show is a short performance which is one of several in the show.

If someone who has been behaving badly cleans up their act, they start to behave in a more acceptable or responsible way.

If you get in on the act, you take part in or take advantage of something that was started by someone else.

You say that someone was in the act of doing something to indicate what they were doing when they were seen or interrupted.

If you get your act together, you organize your life or your affairs so that you are able to achieve what you want or to deal with something effectively.