Longman Dictionary of Contemporary English homepage

act

2 verb
     
Related topics: Performing
act2 S2 W1
1

do something

[intransitive] to do something in a particular way or for a particular reason:
The company acted correctly in sacking him.
The jury decided that Walker had acted in self-defence.
act to do something
The UN must act now to restore democracy.
Politicians will only act when enough people demand that they do something.
2

behave

[intransitive always + adverb/preposition] to behave in a particular way:
They acted unreasonably when they turned down Jill's application.
He's been acting strangely ever since his Mom died.
act as if
Pip acted as if he was better than everyone else.
act like
Stop acting like a baby.
act with
She acted with dignity.
act your age (=used to tell someone to behave in a more adult way, suitable for someone of their age)
3

pretend

[intransitive and transitive] to pretend to have feelings, qualities etc that are different from your true ones:
When he's angry, he acts the fool.
That guy is acting crazy.
act a part/role
Stella felt unnatural in their company, as if she was acting a part.
act as if/like
Why does he act as if he was stupid?
4

play/film

AP [intransitive and transitive] to perform in a play or film:
I first started acting when I was 12 years old.
act a part/role
She is acting the role of Lady Macbeth six evenings a week.
The movie is very well acted.
5

have an effect

[intransitive] to have an effect or use
act as
The padding acts as a cushion if the player falls or is hit by the ball.
act on
Disinfectants act on bacteria in two main ways.
6

act for somebody/act on somebody's behalf

SCL to represent someone, especially in a court of law or by doing business for them:
Makin, a solicitor, is acting for the young people in their case against the county council.
I am acting on behalf of the bank.
 ➔ acting1

act as something

phrasal verb
to do a particular job for a short time, for example while the usual person is absent:
My brother speaks French - he can act as interpreter.

act on/upon something

phrasal verb
to do something because of another person's advice or order, or because you have received information or had an idea:
She is acting on the advice of her lawyers.
Police say they acted on information received.

act something ↔ out

phrasal verb
1AP if a group of people act out an event, they show how it happened by pretending to be the people who were involved in it:
The children were acting out the story of the birth of Jesus.
2 to express your feelings about something through your behaviour or actions, especially when you have been feeling angry or nervous:
These teenagers are likely to act out their distress by running away.

act up

phrasal verb
1 if children act up, they behave badly:
He's a tough kid and he acts up a lot.
2 if a machine or part of your body acts up, it does not work properly:
The computer is acting up again.
Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.

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