Source : Webster's Revised Unabridged Dictionary (1913)

Troop \Troop\, v. t.

   {To troop the} {colors or colours} (Mil.), in the British
      army, to perform a ceremony consisting essentially in
      carrying the colors, accompained by the band and escort,
      slowly before the troops drawn up in single file and
      usually in a hollow square, as in London on the
      sovereign's birthday. Trooper \Troop"er\, n.
   A mounted policeman. [Australia]

   Note: The {black troopers} of Queensland are a regiment of
         aboriginal police, employed chiefly for dispersing wild
         aborigines who encroach on sheep runs.

Trooper \Troop"er\, n.
   A soldier in a body of cavalry; a cavalryman; also, the horse
   of a cavalryman.

Source : WordNet®

trooper
     n 1: a soldier in a motorized army unit [syn: {cavalryman}]
     2: a mounted policeman
     3: a state police officer [syn: {state trooper}]
     4: a soldier mounted on horseback; "a cavalryman always takes
        good care of his mount" [syn: {cavalryman}]