The Collaborative International Dictionary of English v.0.48:

Grouper \Group"er\, n. [Corrupted fr. Pg. garupa crupper. Cf.
   Garbupa.] (Zool.)
   (a) One of several species of valuable food fishes of the
       genus Epinephelus, of the family Serranid[ae], as the
       red grouper, or brown snapper (Epinephelus morio), and
       the black grouper, or warsaw (Epinephelus nigritus),
       both from Florida and the Gulf of Mexico.
   (b) The tripletail (Lobotes).
   (c) In California, the name is often applied to the
       rockfishes. [Written also groper, gruper, and
       trooper.]
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Trooper \Troop"er\, n.
   1. A soldier in a body of cavalry; a cavalryman; also, the
      horse of a cavalryman.
      [1913 Webster]

   2. A state police officer; -- also called state trooper.
      [U. S.]
      [PJC]

   3. 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.
         [Webster 1913 Suppl.]

   4. Trouper.
      [PJC]

   like a trooper, with energy, endurance, or enthusiasm; as,
      to work like a trooper.

WordNet (r) 3.0 (2006):

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