pontoon

plural pontoons

1. A flat-bottomed boat or other floating structure used as a buoyant support for a temporary bridge, dock or landing stage.

   1 more example

   Thanks to the previous experience of the chief performers, to careful preparation and rehearsal, and to perfect weather conditions, they watched in breath-bated silence the spectacle of the huge bulk moving without a hitch into position over the temporary pier caps on which it settled as water ballast was admitted to the pontoons.

   1959 May 28, L. T. C. Rolt, “Centenary of the Royal Albert Bridge at Saltash”, in Railway Magazine, page 310

2. broadlyA bridge with floating supports.

   Synonyms: pontoon bridge

3. A box used to raise a sunken vessel.

   Near-synonyms: caisson, camel, sea camel

   Synonyms: caisson, camel, sea camel

4. A float of a seaplane.
5. A lighter or barge used for loading or unloading ships.

plural pontoons

1. uncountablecard gamesA card game in which the object is to obtain cards whose value adds up to, or nearly to, 21 but not exceed it.

   Synonyms: vingt-et-un

2. countablecard gamesA two-card hand totalling 21 in this game.

   Synonyms: natural