1. The process of doing or performing something: the act of thinking.
a. Something done or performed; a deed: a charitable act.
b. Law Something done that has legal significance: a criminal act.
3. A statute or other law formally adopted by a legislative body: an act of Congress.
4. A formal written record of proceedings or transactions.
5. One of the major divisions of a play, opera, or film.
a. A performance or entertainment usually forming part of a longer presentation: a juggling act; a magic act.
b. The actor or actors presenting such a performance: joined the act in Phoenix.
7. A manifestation of intentional or unintentional insincerity; a pose: put on an act.
v. act·ed, act·ing, acts
1. To play the part of; assume the dramatic role of: She plans to act Ophelia in summer stock.
2. To perform (a role) on the stage: act the part of the villain.
a. To behave like or pose as; impersonate: Don't act the fool.
b. To behave in a manner suitable for: Act your age.
1. To behave or comport oneself: She acts like a born leader.
2. To perform in a dramatic role or roles.
3. To be suitable for theatrical performance: This scene acts well.
4. To behave affectedly or unnaturally; pretend.
5. To appear or seem to be: The dog acted ferocious.
6. To carry out an action: We acted immediately. The governor has not yet acted on the bill.
7. To operate or function in a specific way: His mind acts quickly.
8. To serve or function as a substitute for another: A coin can act as a screwdriver.
9. To produce an effect: waited five minutes for the anesthetic to act.
1. To perform in or as if in a play; represent dramatically: act out a story.
2. To realize in action: wanted to act out his theory.
3. To engage in socially inappropriate or impulsive behavior as a manifestation of psychological or emotional pain or turmoil.
1. To misbehave.
2. To malfunction.
3. Informal To become active or troublesome after a period of quiescence: My left knee acts up in damp weather. Her arthritis is acting up again.
be in on the act
To be included in an activity.
clean up (one's) act Slang
To improve one's behavior or performance.
get into the act
To insert oneself into an ongoing activity, project, or situation.
get (one's) act together Slang
To get organized.
[Middle English, from Old French acte, from Latin āctus, a doing, and āctum, a thing done, both from past participle of agere, to drive, do; see ag- in the Appendix of Indo-European roots.]
Usage Note: Act and action both mean "a deed" and "the process of doing." However, other senses of act, such as "a decision made by a legislative body" and of action, such as "habitual or vigorous activity" show that act tends to refer to a deed while action tends to refer to the process of doing. Thus, people engage in sex acts but not sex actions. By the same token, one may want a piece of the action, but not a piece of the act. The demands of meaning or idiom often require one word or the other. In some cases, either can be used: my act (or action) was premature.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.