/ pɒnˈtuːn; NAmE pɑːn-/ noun
1.
[ C ] a temporary floating platform built across several boats or hollow structures, especially one used for tying boats to
2.
[ C ] a boat or hollow structure that is one of several used to support a floating platform or bridge :
a pontoon bridge
3.
[ U ] ( BrE ) = blackjack
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WORD ORIGIN
sense 3 early 20th cent.: probably an alteration of vingt-et-un twenty-one.
senses 1 to 2 late 17th cent.: from French ponton , from Latin ponto , ponton- , from pons , pont- bridge.