Real Dictionary

act
countable noun: An act in a play, opera, or ballet is one of the main parts into which it is divided.
countable noun: An act in a show is a short performance which is one of several in the show.
countable noun: An Act is a law passed by the government.
countable noun: An act is a single thing that someone does.
singular noun: If you say that someone's behaviour is an act, you mean that it does not express their real feelings.
verb: If a force or substance acts on someone or something, it has a certain effect on them.
verb: If someone acts in a particular way, they behave in that way.
verb: If someone acts in a particular way, they pretend to be something that they are not.
verb: If someone or something acts as a particular thing, they have that role or function.
verb: If you act on advice or information, you do what has been advised or suggested.
verb: If you act, or act a part in a play or film, you have a part in it.
verb: When professionals such as lawyers act for you, or act on your behalf, they are employed by you to deal with a particular matter.
verb: When you act, you do something for a particular purpose.

ACT in American English
abbreviation: American College Test

act in American English 1
a thing done; deed
noun: anything done, being done, or to be done; deed; performance

act in American English 2
active
abbreviation: acting

act in British English
noun: something done or performed; a deed

ACT in British English 1
abbreviation for: Australian Capital Territory

ACT in British English 2
noun acronym for: (in New Zealand) Association of Consumers and Taxpayers: a small political party of the right