Caisson

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.
a boatlike structure used as a gate for a dock or the like.
Nautical.

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.
a watertight structure built against a damaged area of a hull to render the hull watertight; cofferdam.

a two-wheeled wagon, used for carrying artillery ammunition.
an ammunition chest.
a wooden chest containing bombs or explosives, used formerly as a mine.
Architecture, coffer (def 4).
Historical Examples

Battery E in France Frederic R. Kilner
The Long Roll Mary Johnston
Transactions of the American Society of Civil Engineers, vol. LXVIII, Sept. 1910 James H. Brace, Francis Mason and S. H. Woodard
The Long Roll Mary Johnston
An Artilleryman’s Diary Jenkin Lloyd Jones
My Days and Nights on the Battle-Field Charles Carleton Coffin
Diary of Battery A, First Regiment Rhode Island Light Artillery Theodore Reichardt
The Modern Railroad Edward Hungerford
Memoirs of a Veteran Who Served as a Private in the 60’s in the War Between the States Isaac Hermann
The Modern Railroad Edward Hungerford

noun
a watertight chamber open at the bottom and containing air under pressure, used to carry out construction work under water
a similar unpressurized chamber
a watertight float filled with air, used to raise sunken ships See also camel (sense 2)
a watertight structure placed across the entrance of a basin, dry dock, etc, to exclude water from it

a box containing explosives, formerly used as a mine
an ammunition chest
a two-wheeled vehicle containing an ammunition chest

another name for coffer (sense 3)
n.