An Etymological Dictionary of Astronomy and Astrophysics

The intercommunicating body of salt water occupying the depressions of the Earth’s surface, or one of its major primary subdivisions, bounded by the continents, or the equator, and other imaginary lines. A sea is subdivision of an ocean.

the vast body of salt water that covers almost three fourths of the earth’s surface.

Etymology (EN): M.E. ocean(e), from O.Fr. occean, 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.

Etymology (PE): Oqyânus, from Ar., ultimately from Gk., as above.