What is the X in X-mas?
watertight costume for underwater use, connected to the surface or to a diving bell by a tube that provides the wearer with air. The suit, invented early in the 19th century, consists of a watertight covering, weighted boots, and a metal helmet with transparent portholes and provision for air. Suits of articulated armour that do not require decompression have been developed. Diving suits have been supplanted in some applications by scuba-diving equipment.