caisson

noun

• An enclosure from which water can be expelled, in order to give access to underwater areas for engineering works etc.
• The gate across the entrance to a dry dock.
• A floating tank that can be submerged, attached to an underwater object and then pumped out to lift the object by buoyancy; a camel.
• A two-wheeled, horse-drawn military vehicle used to carry ammunition (and a coffin at funerals).
• A large box to hold ammunition.
• A chest filled with explosive materials, used like a mine.
• A coffer.