caisson

American  

[key-suhn, -son] / ˈkeɪ sən, -sɒn /

noun

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.

   1. 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.

   2. 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.

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caisson British  

/ ˈkeɪsən, kəˈsuːn /

noun

1. a watertight chamber open at the bottom and containing air under pressure, used to carry out construction work under water

2. a similar unpressurized chamber

3. a watertight float filled with air, used to raise sunken ships See also camel

4. a watertight structure placed across the entrance of a basin, dry dock, etc, to exclude water from it

5. 1. a box containing explosives, formerly used as a mine

   2. an ammunition chest

   3. a two-wheeled vehicle containing an ammunition chest

6. another name for coffer

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Other Word Forms

• caissoned adjective

Etymology

Origin of caisson

1695–1705; < French, Middle French < Old Provençal, equivalent to caissa box ( case ² ) + -on augmentative suffix

Example Sentences

For years, members of the tiny preservation society — their ages now ranging from 60s to 80s — have flown out in helicopters, landing on the caisson.

From Los Angeles Times • Oct. 26, 2025

Eyer’s body in a flag-draped coffin was brought from police headquarters on a horse-drawn caisson three blocks to the church where the late evangelist Billy Graham held his first crusade.

From Seattle Times • May 3, 2024

They saluted, too, as the flag-draped caisson, drawn by six gray horses, drew forward.

From Washington Post • Sep. 6, 2022

On November 11, 1921, the Unknown was placed on a horse-drawn caisson and carried in a procession through Washington, D.C. and across the Potomac River.

From Fox News • Oct. 4, 2021

Eads discovered that workers began experiencing the bends at sixty feet below ground, roughly half the depth to which a Chicago caisson would have to descend.

From "The Devil in the White City" by Erik Larson