caisson

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A watertight structure within which construction work is carried on under water.
• noun A large box open at the top and one side, designed to fit against the side of a ship and used to repair damaged hulls under water.
• noun A floating structure used to close off the entrance to a dock or canal lock.
• noun A horse-drawn vehicle, usually two-wheeled, used to carry artillery ammunition and coffins at military funerals.
• noun A large box used to hold ammunition.

from The Century Dictionary.

• noun Milit.: A wooden chest into which several bombs are put, and sometimes gunpowder, to be exploded in the way of an enemy or under some work of which he has gained possession.
• noun An ammunition-wagon; also, an ammunition-chest.
• noun In architecture, a sunken panel in a coffered ceiling or in the soffit of Roman or Renaissance architecture, etc.; a coffer; a lacunar. See cut under coffer.
• noun In civil engineering: A vessel in the form of a boat, used as a flood-gate in docks.
• noun An apparatus on which vessels may be raised and floated; especially, a kind of floating dock, which may be sunk and floated under a vessel's keel, used for docking vessels at their moorings, without removing stores or masts. (See floating dock, under dock.)
• noun A water-tight box or casing used in founding and building structures in water too deep for a coffer-dam, such as piers of bridges, quays, etc.

from the GNU version of the Collaborative International Dictionary of English.

• noun A chest to hold ammunition.
• noun A four-wheeled carriage for conveying ammunition, consisting of two parts, a body and a limber. In light field batteries there is one caisson to each piece, having two ammunition boxes on the body, and one on the limber.
• noun A chest filled with explosive materials, to be laid in the way of an enemy and exploded on his approach.
• noun A water-tight box, of timber or iron within which work is carried on in building foundations or structures below the water level.
• noun A hollow floating box, usually of iron, which serves to close the entrances of docks and basins.
• noun A structure, usually with an air chamber, placed beneath a vessel to lift or float it.
• noun (Arch.) A sunk panel of ceilings or soffits.
• noun (Engin.) a caisson, closed at the top but open at the bottom, and resting upon the ground under water. The pressure of air forced into the caisson keeps the water out. Men and materials are admitted to the interior through an air lock. See Lock.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun engineering An enclosure, from which water can be expelled, in order to give access to underwater areas for engineering works etc.
• noun The gate across the entrance to a dry dock.
• noun nautical A floating tank that can be submerged, attached to an underwater object and then pumped out to lift the object by buoyancy; a camel.
• noun military A two-wheeled, horse-drawn military vehicle used to carry ammunition (and a coffin at funerals).
• noun military A large box to hold ammunition.
• noun architecture A variant of coffer.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun large watertight chamber used for construction under water
• noun an ornamental sunken panel in a ceiling or dome
• noun a chest to hold ammunition
• noun a two-wheeled military vehicle carrying artillery ammunition