Webster's Revised Unabridged Dictionary · 1913

Platoon

Platoon , noun

[French peloton a ball of thread, a knot or group of men, a platoon, from pelote a ball formed of things wound round. See Pellet.]

(a)
(Military) Formerly, a body of men who fired together; also, a small square body of soldiers to strengthen the angles of a hollow square.
(b)
(Military) Now, in the United States service, half of a company.