SEA (in O. Eng. sae, a common Teutonic word; cf. Ger. See, Dutch Zee, &c.; the ultimate source is uncertain), in its widest sense that part of the surface of the globe which consists of salt water, in distinction from dry land. The greater divisions of “the sea,” in this sense, are called oceans, and are dealt with under the heading Ocean and Oceanography, the latter being the term now generally applied to the scientific study of the sea. The word “sea,” however, is also used, in a restricted sense, in application to specific parts of the great oceans, more or less clearly defined by a partial land-boundary. Such are the Mediterranean Sea and the Caribbean Sea, connected with the Atlantic Ocean; the Arabian Sea, a division of the Indian Ocean, and the China and Japan Seas of the western Pacific Ocean. Subdivisions of great seas are similarly defined (e.g. the Adriatic Sea), and a few large bodies of salt water entirely land-locked are also called seas—e.g. the Caspian Sea, the Sea of Aral, the Dead Sea. Sea-level is the assumed mean level of the sea, serving as a datum from which to calculate the elevation of land in surveying (q.v.).