The Collaborative International Dictionary of English v.0.48:

Troop \Troop\, n. [F. troupe, OF. trope, trupe, LL. troppus; of
   uncertain origin; cf. Icel. [thorn]orp a hamlet, village, G.
   dorf a village, dial. G. dorf a meeting. Norw. torp a little
   farm, a crowd, E. thorp. Cf. Troupe.]
   1. A collection of people; a company; a number; a multitude.
      [1913 Webster]

            That which should accompany old age
            As honor, love, obedience, troops of friends
            I must not look to have.              --Shak.
      [1913 Webster]

   2. Soldiers, collectively; an army; -- now generally used in
      the plural.
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            Farewell the plumed troop, and the big wars. --Shak.
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            His troops moved to victory with the precision of
            machines.                             --Macaulay.
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   3. (Mil.) Specifically, a small body of cavalry, light horse,
      or dragoons, consisting usually of about sixty men,
      commanded by a captain; the unit of formation of cavalry,
      corresponding to the company in infantry. Formerly, also,
      a company of horse artillery; a battery.
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   4. A company of stageplayers; a troupe. --W. Coxe.
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   5. (Mil.) A particular roll of the drum; a quick march.
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   6. See Boy scout, above.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Troop \Troop\, v. i. [imp. & p. p. Trooped; p. pr. & vb. n.
   Trooping.]
   1. To move in numbers; to come or gather in crowds or troops.
      "Armies . . . troop to their standard." --Milton.
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   2. To march on; to go forward in haste.
      [1913 Webster]

            Nor do I, as an enemy to peace,
            Troop in the throngs of military men. --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Troop \Troop\, v. t.

   To troop the colors or To troop the colours (Mil.),
   in the British army, to perform a ceremony consisting
   essentially in carrying the colors, accompanied 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.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

troop
    n 1: a group of soldiers
    2: a cavalry unit corresponding to an infantry company
    3: a unit of Girl or Boy Scouts [syn: troop, scout troop,
       scout group]
    4: an orderly crowd; "a troop of children" [syn: troop,
       flock]
    v 1: march in a procession; "the veterans paraded down the
         street" [syn: parade, troop, promenade]
    2: move or march as if in a crowd; "They children trooped into
       the room"

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "troop":
   KP, age group, ambulate, armed forces, army, army group,
   assemblage, assembly, band, battalion, battery, battle group, bevy,
   body, brigade, bunch, cabal, cadre, cast, clique, cohort,
   collection, colony, column, combat command, combat team, company,
   complement, contingent, corps, coterie, covey, crew, crowd,
   detachment, detail, division, drift, drive, drove, faction,
   field army, field train, file, fleet, flock, flying column,
   foot it, forces, gam, gang, garrison, gathering, group, grouping,
   groupment, herd, hoof, host, in-group, junta, kennel,
   kitchen police, legion, litter, maniple, military, mob, movement,
   multitude, organization, out-group, outfit, pace, pack, party,
   peer group, phalanx, platoon, pod, posse, pride, rank, regiment,
   salon, school, section, set, shoal, skulk, sloth, soldiers, squad,
   squadron, stable, step, string, tactical unit, task force, team,
   train, traipse, tread, tribe, trip, troopers, troupe, unit, wing