1. 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. 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.
The french spelling ponton often appears in scientific works, but pontoon is more common form.
Origin: F. Ponton (cf. It. Pontone), from L. Ponto, -onis, fr. Pons, pontis, a bridge, perhaps originally, a way, path: cf. Gr. Path, Skr. Path, pathi, panthan. Cf. Punt a boat.