COFFERDAM

caisson, pneumatic caisson, cofferdam

(noun) large watertight chamber used for construction under water

Source: WordNet® 3.1

Etymology

Noun

cofferdam (plural cofferdams)

A temporary watertight structure that is pumped dry to enclose an area underwater and allow construction work on a ship, bridge, or rig to be carried out; a caisson.

(nautical) An empty space that acts as a protective barrier between two floors or bulkheads on a ship.

Source: Wiktionary

Cof"fer*dam, n.

Definition: A water-tight inclosure, as of piles packed with clay, from which the water is pumped to expose the bottom (of a river, etc.) and permit the laying of foundations, building of piers, etc.

Source: Webster’s Unabridged Dictionary 1913 Edition