NOUN (3)

1. a military unit that is a subdivision of a company; usually has a headquarters and two or more squads; usually commanded by a lieutenant;

2. a team of policemen working under the military platoon system;

3. a group of persons who are engaged in a common activity;
- Example: "platoons of tourists poured out of the busses"
- Example: "the defensive platoon of the football team"

The Collaborative International Dictionary of English v.0.48:

Platoon \Pla*toon"\, n. [F. peloton a ball of thread, a knot or
   group of men, a platoon, from pelote a ball formed of things
   wound round. See Pellet.] (Mil.)
   (a) Formerly, a body of men who fired together; also, a small
       square body of soldiers to strengthen the angles of a
       hollow square.
   (b) Now, in the United States service, half of a company.
       [1913 Webster]

WordNet (r) 3.0 (2006):

platoon
    n 1: a military unit that is a subdivision of a company; usually
         has a headquarters and two or more squads; usually
         commanded by a lieutenant
    2: a team of policemen working under the military platoon system
    3: a group of persons who are engaged in a common activity;
       "platoons of tourists poured out of the busses"; "the
       defensive platoon of the football team"

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "platoon":
   KP, age group, army, army group, array, band, batch, battalion,
   battery, battle group, bevy, body, brigade, bunch, cabal, cadre,
   cast, clique, clump, cluster, cohort, column, combat command,
   combat team, company, complement, contingent, corps, coterie,
   covey, crew, crowd, detachment, detail, division, eight, eleven,
   faction, field army, field train, file, first string, first team,
   five, fleet, flying column, formation, gang, garrison, group,
   grouping, groupment, in-group, junta, kitchen police, legion, lot,
   maniple, mob, movement, nine, organization, out-group, outfit,
   pack, parcel, party, patrol, peer group, phalanx, posse, rank,
   regiment, reserves, rowing crew, salon, second string, second team,
   section, set, squad, squadron, stable, string, tactical unit,
   task force, team, third string, train, tribe, troop, troupe, unit,
   varsity, wing