Caisson

n.	1.	(Mil.) A chest to hold ammunition.
	2.	A water-tight box, of timber or iron within which work is carried on in building foundations or structures below the water level.
	3.	(Arch.) A sunk panel of ceilings or soffits. Pneumatic caisson (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.

Noun	1.	caisson - an ornamental sunken panel in a ceiling or dome Synonyms: coffer, lacuna
	2.	caisson - a two-wheeled military vehicle carrying artillery ammunition
	3.	caisson - a chest to hold ammunition Synonyms: ammunition chest
	4.	caisson - large watertight chamber used for construction under water Synonyms: cofferdam, pneumatic caisson

coffer, lacuna, panel