Pontoon (noun)

A flat-bottomed boat or buoyant device used as a support for a temporary bridge or pier.

Origin:

Early 18th century (denoting a flat-bottomed boat used in building bridges over rivers): from french ponton, from italian ponte "bridge".

Examples:

1. The bridge over the river was built on pontoons.
2. The pontoon boat was anchored in the middle of the lake.
3. The pontoons of the raft were filled with air.
4. The pontoons of the floatplane were inflated and ready for takeoff.
5. They used pontoons to make a temporary bridge to cross the river.