cais·son 
(k
s
n
, -s
n)
KEY NOUN:
- A watertight structure within which construction work is carried on under water.
- See camel.
- 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.
- A floating structure used to close off the entrance to a dock or canal lock.
- A horse-drawn vehicle, usually two-wheeled, used to carry artillery ammunition and coffins at military funerals.
- A large box used to hold ammunition.
ETYMOLOGY:French, from Old French,
large box, alteration (influenced by
caisse,
chest), of
casson from Italian
cassone, augmentative of
cassa,
box, from Latin
capsa
