Act \Act\, v. i.

1. To exert power; to produce an effect; as, the stomach acts upon food.

2. To perform actions; to fulfill functions; to put forth energy; to move, as opposed to remaining at rest; to carry into effect a determination of the will.

He hangs between, in doubt to act or rest. --Pope.

3. To behave or conduct, as in morals, private duties, or public offices; to bear or deport one's self; as, we know not why he has acted so.

4. To perform on the stage; to represent a character.

To show the world how Garrick did not act. --Cowper.

To act as or for, to do the work of; to serve as.

To act on, to regulate one's conduct according to.

To act up to, to equal in action; to fulfill in practice; as, he has acted up to his engagement or his advantages.

Source: Webster's Revised Unabridged Dictionary (1913)