pon·toon¹ / ˌpänˈtoōn/ • n. a flat-bottomed boat or hollow metal cylinder used with others to support a temporary bridge or floating landing stage. ∎  a bridge or landing stage supported by pontoons. ∎  a large flat-bottomed barge or lighter equipped with cranes. ∎  either of the floats fitted to an aircraft to enable it to land on water.

pontoons

pontoon1 boat (or other vessel), of which a number are used to support a temporary bridge. XVII (ponton). — (O)F. ponton :— L. pontō, -ōn- punt, bridge of boats, f. pōns, pont- bridge, rel. to Indo-Iran. and Balto-Slav. words, with Gr. pátos, meaning ‘road’, ‘path’, but the relevance of the sense in PONTIFF (if this is ‘path-maker’) is not clear; see -OON.

pontoon2 app. alt. of F. vingt-(et-)un ‘twenty-one’ (card game). XX.