a. a watertight float or vessel used where buoyancy is required in water, as in supporting a bridge, in salvage work, or where a temporary or mobile structure is required in military operations
b. (as modifier): a pontoon bridge
2.
nautical a float, often inflatable, for raising a vessel in the water
[C17: from French ponton, from Latin pontō punt, floating bridge, from pōns bridge]
pontoon2 (pɒnˈtuːn)
—n
1.
twenty-one, Also called: vingt-et-un a gambling game in which players try to obtain card combinations worth 21 points
2.
(in this game) the combination of an ace with a ten or court card when dealt to a player as his first two cards
[C20: probably an alteration of French vingt-et-un, literally: twenty-one]
1676, from Fr. pontoon, from M.Fr. ponton, from L. pontonem (nom. ponto) "flat-bottomed boat," from pons "bridge." Pontoon bridge is first recorded 1778.