The Collaborative International Dictionary of English v.0.48:

Act \Act\ ([a^]kt), n. [L. actus, fr. agere to drive, do: cf. F.
   acte. See Agent.]
   1. That which is done or doing; the exercise of power, or the
      effect, of which power exerted is the cause; a
      performance; a deed.
      [1913 Webster]

            That best portion of a good man's life,
            His little, nameless, unremembered acts
            Of kindness and of love.              --Wordsworth.
      [1913 Webster] Hence, in specific uses:
      (a) The result of public deliberation; the decision or
          determination of a legislative body, council, court of
          justice, etc.; a decree, edit, law, judgment, resolve,
          award; as, an act of Parliament, or of Congress.
      (b) A formal solemn writing, expressing that something has
          been done. --Abbott.
      (c) A performance of part of a play; one of the principal
          divisions of a play or dramatic work in which a
          certain definite part of the action is completed.
      (d) A thesis maintained in public, in some English
          universities, by a candidate for a degree, or to show
          the proficiency of a student.
          [1913 Webster]

   2. A state of reality or real existence as opposed to a
      possibility or possible existence. [Obs.]
      [1913 Webster]

            The seeds of plants are not at first in act, but in
            possibility, what they afterward grow to be.
                                                  --Hooker.
      [1913 Webster]

   3. Process of doing; action. In act, in the very doing; on
      the point of (doing). "In act to shoot." --Dryden.
      [1913 Webster]

            This woman was taken . . . in the very act. --John
                                                  viii. 4.
      [1913 Webster]

   Act of attainder. (Law) See Attainder.

   Act of bankruptcy (Law), an act of a debtor which renders
      him liable to be adjudged a bankrupt.

   Act of faith. (Ch. Hist.) See Auto-da-F['e].

   Act of God (Law), an inevitable accident; such
      extraordinary interruption of the usual course of events
      as is not to be looked for in advance, and against which
      ordinary prudence could not guard.

   Act of grace, an expression often used to designate an act
      declaring pardon or amnesty to numerous offenders, as at
      the beginning of a new reign.

   Act of indemnity, a statute passed for the protection of
      those who have committed some illegal act subjecting them
      to penalties. --Abbott.

   Act in pais, a thing done out of court (anciently, in the
      country), and not a matter of record.
      [1913 Webster]

   Syn: See Action.
        [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ACT IN PAIS. An act performed out of court, and not a matter of record.
Pais, in law French, signifies country. A deed or an assurance transacted
between two or more private persons in the country is matter in pais. 2 Bl.
Com. 294.