[pon.toon] n [F ponton, fr. L ponton-, ponto] (1690) 1: a flat-bottomed boat (as a lighter); esp: a flat-bottomed boat or portable float used in building a floating temporary bridge
2: a float esp. of a seaplane
[2]pontoon n [perh. alter. of vingt-et-un] (ca. 1917) Brit: blackjack
5.