Caisson

1. n. A sunk panel of ceilings or soffits.
2. n. A chest to hold ammunition.
3. n. 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.
4. n. A chest filled with explosive materials, to be laid in the way of an enemy and exploded on his approach.
5. n. A water-tight box, of timber or iron within which work is carried on in building foundations or structures below the water level.
6. n. A hollow floating box, usually of iron, which serves to close the entrances of docks and basins.
7. n. A structure, usually with an air chamber, placed beneath a vessel to lift or float it.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.