noun

1. a watertight temporary structure in a river, lake, etc., for keeping the water from an enclosed area that has been pumped dry so that a bridge foundation, dam, or pier may be constructed
2. a watertight box or chamber attached to the side of a ship so that repairs can be made below the waterline
3. an empty space serving as a protective barrier, as between two compartments of a ship

Etymology: coffer + dam