Main Entry: cais·son

Pronunciation: \ˈkā-ˌsän, -s^ən, British also kə-ˈsün\

Function: noun

Etymology: French, from Middle French, from Old Occitan, from caissa chest, from Latin capsa — more at case

Date: circa 1702

1 a : a chest to hold ammunition b : a usually 2-wheeled vehicle for artillery ammunition attachable to a horse-drawn limber; also : a limber with its attached caisson
2 a : a watertight chamber used in construction work under water or as a foundation b : a hollow floating box or a boat used as a floodgate for a dock or basin
3 : coffer 3

[caisson illustration]