troop / troōp/ • n. 1. a group of soldiers, esp. a cavalry unit commanded by a captain, or an airborne unit. ∎  (troops) soldiers or armed forces: UN peacekeeping troops | [as adj.] (troop) troop withdrawals. ∎  a unit of 18 to 24 Girl Scouts or Boy Scouts organized under a troop leader.2. a group of people or animals of a particular kind: a troop of musicians.• v. [intr.] (of a group of people) come or go together or in large numbers: the girls trooped in for dinner. ∎  (of a lone person) walk at a slow or steady pace: Caroline trooped wearily home from work.

troop body of soldiers, (pl.) armed forces; number of persons collected together XVI; signal on a drum for assembling troops XVII. — F. troupe, poss. back-formation from troupeau flock, herd, dim. f. medL. troppus herd of mares, prob. of Gmc. orig.
Hence troop vb. gather in a troop XVI; t. the colour beat the drum for the reception of the colour at the mounting of the guard XVII. trooper (-ER1) cavalry soldier. XVII.