Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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"