cais·son /ˈkeɪsən, -sɒn/

1. a structure used in underwater work, consisting of an airtight chamber, open at the bottom and containing air under sufficient pressure to exclude the water.
2. a boatlike structure used as a gate for a dock or the like.
3. Nautical .
a. Also called camel, pontoon. a float for raising a sunken vessel, sunk beside the vessel, made fast to it, and then pumped out to make it buoyant.
b. a watertight structure built against a damaged area of a hull to render the hull watertight; cofferdam.
4. a two-wheeled wagon, used for carrying artillery ammunition.
5. an ammunition chest.
6. a wooden chest containing bombs or explosives, used formerly as a mine.
7. Architecture . coffer ( def. 4 ) .

1695–1705; < F, MF < OPr, equiv. to caissa box ( see case 2 ) + –on aug. suffix

—Related forms
caissoned, adjective


(2) thoracic: the rusting shells of U-boats beached in the cove at Tsingtao, near the ruined German forts where the Chinese guides smeared bloody handprints on the caisson walls;

Source: The Atrocity Exhibition by J G Ballard.