<p><strong>Verb (used with object)</strong></p><ul><li>to do something; exert energy or force; be employed or operative: He acted promptly in the emergency.</li><li>to reach, make, or issue a decision on some matter: I am required to act before noon tomorrow.</li><li>to represent (a fictitious or historical character) with one's person: to act Macbeth.</li><li>Synonyms: play, work, function, perform.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>to behave or conduct oneself in a particular fashion: to act well under all conditions.</li><li>to pretend; feign: Act interested even if you're bored.</li><li>to perform as an actor: He acted in three plays by Molière.</li><li>to be capable of being performed: His plays don't act well.</li><li>to serve or substitute (usually followed by for): In my absence the assistant manager will act for me.</li></ul><p><strong>Verb Phrase</strong></p><ul><li>to fail to function properly; malfunction: The vacuum cleaner is acting up again.</li><li>to behave willfully: The children always act up in school the day before a holiday.</li><li>to become painful or troublesome, especially after a period of improvement or remission: My arthritis is acting up again this morning.</li><li>Informal: to organize one's time, job, resources, etc., so as to function efficiently: The new administration is still getting its act together.</li><li>to act in accordance with; follow: He acted on my advice.</li><li>to have an effect on; affect: The stirring music acted on the emotions of the audience.</li><li>to demonstrate or illustrate by pantomime or by words and gestures: The party guests acted out stories for one another.</li><li>Psychology: to give overt expression to (repressed emotions or impulses) without insightful understanding: The patients acted out early traumas by getting angry with the analyst.</li></ul>