WordWeight : Weighing the Words

Pronunciation : Pon*toon"
Part of Speech : n.
Etymology : [F. ponton (cf. It. pontone), from L. ponto, - onis, fr. pons, pontis, a bridge, perhaps originally, a way, path: cf. Gr. path, pathi, panthan. Cf. Punt a boat.]
Definition : 1. (Mil.)

Defn: A wooden flat-bottomed boat, a metallic cylinder, or a frame covered with canvas, India rubber, etc., forming a portable float, used in building bridges quickly for the passage of troops.

2. (Naut.)

Defn: A low, flat vessel, resembling a barge, furnished with cranes, capstans, and other machinery, used in careening ships, raising weights, drawing piles, etc., chiefly in the Mediterranean; a lighter. Pontoon bridge, a bridge formed with pontoons. -- Pontoon train, the carriages of the pontoons, and the materials they carry for making a pontoon bridge.

Note: The French spelling ponton often appears in scientific works, but pontoon is more common form.
Source : Webster's Unabridged Dictionary, 1913