act \act\, v. i.
   1. to exert power; to produce an effect; as, the stomach acts
      upon food.
      1913 webster

   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.
      1913 webster

            he hangs between, in doubt to act or rest. --pope.
      1913 webster

   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.
      1913 webster

   4. to perform on the stage; to represent a character.
      1913 webster

            to show the world how garrick did not act. --cowper.
      1913 webster

   to act as or to act 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.
      1913 webster
see also:
to act as to act for to act on to act up to