v.
    - take action; do something. ▸
(act up)
 informal behave badly. 
- 
(act for/on behalf of)
 represent on a contractual or legal basis. ▸
[as adj. acting]
 temporarily doing the duties of another. 
- take effect or have a particular effect.
- perform a fictional role in a play or film. ▸behave so as to appear to be: ![]()  I acted dumb. 
▸
(act something out)
 perform a narrative as if it were a play. 
n.
      - a thing done.
- a simulation or pretence. ▸a particular type of behaviour or routine: ![]()  he did his Sir Galahad act. 
- Law  a written ordinance of Parliament, Congress, etc.
- dated a record of the decisions or proceedings of a committee or an academic body.
- a main division of a play, ballet, or opera.
- a set performance:![]()  her one-woman poetry act. 
Phrase
  
    - act of God
 an instance of uncontrollable natural forces in operation.
- act of grace
 a privilege or concession that cannot be claimed as a right.
- get 
(or be)
 in on the act
 informal become (or be) involved in a particular activity, in order to gain an advantage.
 
  Derivative
  
    - actability n.
- actable adj.
- acting n.
 
  Etymology
  ME: from L. actus ‘event, thing done’, from act-, agere ‘do, act’, reinforced by Fr. acte.