Source : Webster's Revised Unabridged Dictionary (1913)

Coup \Coup\ (k[=oo]), n.
   1. A single roll of the wheel at roulette, or a deal at rouge
      et noir. [Cant]

   2. Among some tribes of North American Indians, the act of
      striking or touching an enemy in warfare with the hand or
      at close quarters, as with a short stick, in such a manner
      as by custom to entitle the doer to count the deed an act
      of bravery; hence, any of various other deeds recognized
      by custom as acts of bravery or honor.

            While the coup was primarily, and usually, a blow
            with something held in the hand, other acts in
            warfare which involved great danger to him who
            performed them were also reckoned coups by some
            tribes.                               --G. B.
                                                  Grinnell.

            Among the Blackfeet the capture of a shield, bow,
            gun, war bonnet, war shirt, or medicine pipe was
            deemed a coup.                        --G. B.
                                                  Grinnell.

Coup \Coup\ v. i.
   To make a coup.

         Woe to the Sioux if the Northern Cheyennes get a chance
         to coup !                                --F.
                                                  Remington.

Coup \Coup\ (k??), n. [F., fr.L. colaphus a cuff, Gr. ????.]
   A sudden stroke; an unexpected device or stratagem; -- a term
   used in various ways to convey the idea of promptness and
   force.

   {Coup de grace} (k??" de gr?s") [F.], the stroke of mercy
      with which an executioner ends by death the sufferings of
      the condemned; hence, a decisive, finishing stroke.

   {Coup de main} (k??` de m?n`) [F.] (Mil.), a sudden and
      unexpected movement or attack.

   {Coup de soleil} (k??` d s?-l?l or -l?"y') [F.] (Med.), a
      sunstroke. See {Sunstroke}.

   {Coup d'['e]tat} (k??" d?-t?") [F.] (Politics), a sudden,
      decisive exercise of power whereby the existing government
      is subverted without the consent of the people; an
      unexpected measure of state, more or less violent; a
      stroke of policy.

   {Coup d'[oe]il} (k[=oo]` d[~e]l"). [F.]
   (a) A single view; a rapid glance of the eye; a comprehensive
       view of a scene; as much as can be seen at one view.
   (b) The general effect of a picture.
   (c) (Mil.) The faculty or the act of comprehending at a
       glance the weakness or strength of a military position,
       of a certain arrangement of troops, the most advantageous
       position for a battlefield, etc.

Source : WordNet®

coup
     n 1: a sudden and decisive change of government illegally or by
          force [syn: {coup d'etat}, {putsch}, {takeover}]
     2: a brilliant and notable success