Act

Old French acte, from Latin Äcta ("register of events"), plural of Äctum ("decree, law"), from agÅ ("put in motion").

Full definition of act

(countable and uncountable; plural acts)

WordsworthThat best portion of a good man's life,
His little, nameless, unremembered acts
Of kindness and of love.

HookerThe seeds of plants are not at first in act, but in possibility, what they afterward grow to be.

2012-03, William E. Carter, Merri Sue Carter, The British Longitude Act Reconsidered, But was it responsible governance to pass the Longitude Act without other efforts to protect British seamen? Or might it have been subterfugeâ€”a disingenuous attempt to shift attention away from the realities of their life at sea.

1905, w, w:The Case of Miss Elliott Chapter 2, â€œH'm !” he said, “so, so—it is a tragedy in a prologue and three acts. I am going down this afternoon to see the curtain fall for the third time on what ... will prove a good burlesque ; but it all began dramatically enough. It was last Saturday â€¦ that two boys, playing in the little spinney just outside Wembley Park Station, came across three large parcels done up in American cloth. â€¦â€

The pivotal moment in the play was in the first scene of the second act.
(countable) A performer or performers in a show.
Which act did you prefer? The soloist or the band?
(countable) Any organized activity.

1934, Babette Hughes, One egg: a farce in one act, The minute you let it be known you're planning a sales campaign everybody wants to get into the act.

(countable) A display of behaviour.
A thesis maintained in public, in some English universities, by a candidate for a degree, or to show the proficiency of a student.

(intransitive) To do something.If you don't act soon, you will be in trouble.
(obsolete, transitive) To do (something); to perform.

Jeremy Taylorthat we act our temporal affairs with a desire no greater than our necessity
BarrowIndustry doth beget by producing good habits, and facility of acting things expedient for us to do.
CowperUplifted hands that at convenient times
Could act extortion and the worst of crimes.

(intransitive) To perform a theatrical role.I started acting at the age of eleven in my local theatre.
(intransitive) To behave in a certain way.He's acting strangely - I think there's something wrong with him.
(copulative) To convey an appearance of being.He acted unconcerned so the others wouldn't worry.
(intransitive, construed with on or upon) To have an effect (on).High-pressure oxygen acts on the central nervous system and may cause convulsions or death.Gravitational force acts on heavy bodies.
(transitive) To play (a role).He's been acting Shakespearean leads since he was twelve.
(transitive) To feign.He acted the angry parent, but was secretly amused.

(mathematics, intransitive, construed with on or upon, of a group) To map via a homomorphism to a group of automorphisms (of).This group acts on the circle, so it can't be left-orderable!
(obsolete, transitive) To move to action; to actuate; to animate.