sea noun definition in Coastlines and the sea topic from the Oxford Advanced Learner's Dictionary

sea

 noun: Coastlines and the sea topic
1 (also the sea) [uncountable] (literary seas [plural]) (especially British English) the salt water that covers most of the earth’s surface and surrounds its continents and islands to travel by sea a cottage by the sea The waste was dumped in the sea. The wreck is lying at the bottom of the sea. We left port and headed for the open sea (= far away from land). the cold seas of the Arctic a sea voyage a hotel room with sea view2 [countable] (often Sea, especially as part of a name) a large area of salt water that is part of an ocean or surrounded by land the North Sea the Caspian Sea3 [countable] (also seas [plural]) the movement of the waves of the sea It was a calm sea. The sea was very rough.4 [singular] sea of something a large amount of something that stretches over a wide area He looked down at the sea of smiling faces before him.1 on the sea, especially in a ship, or in the sea It happened on the second night at sea. They were lost at sea.2 confused and not knowing what to do I'm all at sea with these new regulations.to become a sailorfar away from land where the sea is deepest She fell overboard and was swept out to sea.to leave a port or harbour by ship or boat