pontoon Meaning, Definition & Usage

  1. noun (nautical) a floating structure (as a flat-bottomed boat) that serves as a dock or to support a bridge
  2. noun a float supporting a seaplane

WordNet

Pon*toon" noun
Etymology
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.
Definitions
  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. ✍ The French spelling ponton often appears in scientific works, but pontoon is more common form.

Webster 1913