ocean

c.1290, from O.Fr. occean (12c.), from L. oceanus, from Gk. okeanos, the great river or sea surrounding the disk of the Earth (as opposed to the Mediterranean), of unknown origin. Personified as Oceanus, son of Uranus and Gaia and husband of Tethys. In early times, when the only known land masses were Eurasia and Africa, the ocean was an endless river that flowed around them. Until c.1650, commonly ocean sea, translating L. mare oceanum. Application to individual bodies of water began 14c.; there are usually reckoned to be five of them, but this is arbitrary; also occasionally applied to smaller subdivisions, e.g. German Ocean "North Sea." Oceanography coined in Eng. 1859, from Gk. graphia, from graphein "to write" (about).