GNU Collaborative International Dictionary of English

Found one definition

1.       
   Pontoon , n. [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.]
   (Mil.) 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.
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   (Naut.) 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.
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   Pontoon bridge, a bridge formed with pontoons. -- Pontoon train, the carriages of the pontoons, and the materials they carry for making a pontoon bridge.
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   ☞ The French spelling ponton often appears in scientific works, but pontoon is more common form.
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