| 1. | anything done, being done, or to be done; deed; performance: a heroic act. |
| 2. | the process of doing: caught in the act. |
| 3. | a formal decision, law, or the like, by a legislature, ruler, court, or other authority; decree or edict; statute; judgment, resolve, or award: an act of Congress. |
| 4. | an instrument or document stating something done or transacted. |
| 5. | one of the main divisions of a play or opera: the second act of Hamlet. |
| 6. | a short performance by one or more entertainers, usually part of a variety show or radio or television program. |
| 7. | the personnel of such a group: The act broke up after 30 years. |
| 8. | false show; pretense; feint: The politician's pious remarks were all an act. |
| 9. | Philosophy. (in scholasticism)
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| 10. | to do something; exert energy or force; be employed or operative: He acted promptly in the emergency. |
| 11. | to reach, make, or issue a decision on some matter: I am required to act before noon tomorrow. |
| 12. | to operate or function in a particular way; perform specific duties or functions: to act as manager. |
| 13. | to produce an effect; perform a function: The medicine failed to act. |
| 14. | to behave or conduct oneself in a particular fashion: to act well under all conditions. |
| 15. | to pretend; feign: Act interested even if you're bored. |
| 16. | to perform as an actor: He acted in three plays by Molière. |
| 17. | to be capable of being performed: His plays don't act well. |
| 18. | to serve or substitute (usually fol. by for): In my absence the assistant manager will act for me. |
| 19. | to represent (a fictitious or historical character) with one's person: to act Macbeth. |
| 20. | to feign; counterfeit: to act outraged virtue. |
| 21. | to behave as: He acted the fool. |
| 22. | Obsolete. to actuate. |
| 23. | act on or upon,
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| 24. | act out,
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| 25. | act up,
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| 26. | get or have one's act together, Informal. to organize one's time, job, resources, etc., so as to function efficiently: The new administration is still getting its act together. |
| 27. | act funny, to display eccentric or suspicious behavior. |
| 28. | act one's age, to behave in a manner appropriate to one's maturity: We children enjoyed our uncle because he didn't always act his age. |
| 29. | clean up one's act, Informal. to begin adhering to more acceptable practices, rules of behavior, etc.: The factory must clean up its act and treat its employees better. |

act out
Perform or portray something or someone, as in As she read to the class, the teacher had each child act out a different character in the story. [c. 1600]
Express unconscious feelings or impulses through one's behavior, without being aware of it. For example, She acted out her anger at her father by screaming at her husband. This meaning comes from 20th-century psychological theory and usually (but not always) refers to negative or hostile impulses and emotions. The term is sometimes used without an object to mean "misbehave" or "behave disruptively," as in The child is acting out in class. [First half of 1900s] In both usages, out means "openly" or "publicly."