means The vast continuous body of saltwater that covers most of Earth's surface, or any of its named divisions like the Pacific or Atlantic.

from From the Greek 'Okeanos', the great river the ancients believed encircled the whole flat disc of the world — and also a Titan, the god of that endless stream. It flowed through Latin as 'oceanus' and into Old French before reaching English. So the word still carries an old idea: not a sea among seas, but the one boundless water wrapped around everything.