Temporarily assuming the duties or authority of another person when they are unable to do their job.

present participle of act

(countable, obsolete) An action or deed. / (law) Something done by a party — so called to avoid confusion with the legal senses of deed and action. / Pretending. / (drama) The occupation of an actor.

plural of acting

Initialism of Australian Capital Territory, a federal territory of Australia. / Initialism of American College Test.

An instance of a certain standardized college admissions test in the United States, originally called the American College Test.

(countable) Something done, a deed. / (obsolete, uncountable) Actuality. / (theology) Something done once and for all, as distinguished from a work.

(intransitive) To do something. / (obsolete, transitive) To do (something); to perform. / (intransitive) To perform a theatrical role. / (intransitive) Of a play: to be acted out (well or badly).

(biblical) Clipping of Acts of the Apostles.

plural of Act.