Definition of sea noun from the Oxford Advanced American Dictionary

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sea

noun
/si/
 
 
1 often the sea [uncountable] (also literary seas [plural]) the salt water that covers most of the earth's surface and surrounds its continents and islandsto travel by seaWe left port and headed for the open sea (= far away from land).the cold seas of the Arctica sea voyagea hotel room with a sea view see also the high seas, ocean2 [countable] (often Sea, especially as part of a name) a large area of salt water that is part of an ocean or surrounded by landthe North Seathe Caspian Sea3 [countable] also seas [plural] the movement of the waves of the oceanIt was a calm sea.The sea was very rough.4 [singular] sea of something a large amount of something that stretches over a wide areaHe looked down at the sea of smiling faces before him.IDIOMS

at sea

1 on the ocean, especially in a ship, or in the oceanIt happened on the second night at sea.They were lost at sea.2 confused and not knowing what to doI'm all at sea with these new regulations.at sea

between the devil and the deep blue sea

in a difficult situation where there are two equally unpleasant or unacceptable choices
between the devil and the deep blue sea

go to sea

to become a sailor
go to sea

out to sea

far away from land where the ocean is deepest
She fell overboard and was swept out to sea.out to sea

put (out) to sea

to leave a port or harbor by ship or boat
put to seaput out to sea

there are plenty of other/more fish in the sea

there are many other people or things that are as good as the one someone has failed to get
there are plenty of other fish in the seathere are plenty of more fish in the sea