[cais.son] n [F, fr. MF, fr. OProv, fr. caissa chest, fr. L capsa--more at case] (ca. 1702) 1 a: a chest to hold ammunition b: a usu. 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