- pontoon - (nautical) a floating structure (as a flat-bottomed boat) that serves as a dock or to support a bridge
--1 is a kind of barge, flatboat, hoy, lighter
--1 is a part of pontoon bridge, bateau bridge, floating bridge- pontoon - a float supporting a seaplane
--2 is a kind of float
--2 is a part of amphibian, amphibious aircraft - pontoon - a float supporting a seaplane