\Pon*toon"\, 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.]
1. (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.
2. (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.
{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.