From Longman Dictionary of Contemporary Englishseasea /siː/ ●●● S2 W1 noun 1 [countable, uncountable]HEO especially British English the large area of salty water that covers much of the Earth’s surface syn ocean Jay stripped his clothes off and ran into the sea. The sea came up to my knees. Most exports went by sea (=on a ship). a little cottage by the sea (=near the sea) He spent over 30 years at sea (=working on ships or boats on the sea). They stood side by side looking out to sea (=looking at the sea).2 [countable]HEO a large area of salty water that is mostly enclosed by land the Mediterranean Sea3 → sea of something4 → (all) at sea5 → the seas6 [countable]HA one of the broad areas that seem flat on the Moon and MarsGRAMMAR: Patterns with seain the sea• You use in the sea to talk about things that happen in the water: We paddled in the sea.Whales are mammals that live in the sea. on the sea• You use on the sea to talk about things that happen on the surface of the water: The boat floated on the calm sea.by the sea• You use by the sea to talk about things that are on the land near the sea: They live in a cottage by the sea.COLLOCATIONSadjectivesblueThe sun shone brightly upon the clear blue sea.calmThe sea was perfectly calm.rough (=with big waves)The sea was too rough to swim in.choppy (=with a lot of small waves)The wind was starting to pick up and the sea was becoming choppy.The yachts bobbed around on the choppy sea.heavy seas (=a rough sea)The tanker split apart and sank in heavy seas.a stormy seaa picture of a battleship in a stormy seathe open sea (=the part of the sea that is far away from land)Rescuers are trying to drive the stranded whales back out into the open sea.the deep sea (=the water deep under the surface of the sea)The deep sea is the most unexplored area left on the planet.verbscross the seaOur ancestors crossed the sea in small boats.go to sea (=go to work on a ship)He went to sea when he was eighteen.put to sea (=sail a boat away from land)The refugees put to sea in rickety rafts.be lost at sea formal (=be drowned in the sea)His father had been lost at sea three months before.be swept out to sea (=be taken far away from land by the sea)They had to rescue three young canoeists who were swept out to sea.sea + NOUNsea waterRemoving salt from sea water is an expensive process.a sea viewAll the bedrooms have a sea view.sea levelAverage sea levels are rising year on year.the sea air (=the air close to the sea)He breathed in the fresh sea air.the sea bed (also the sea floor) (=the land at the bottom of the sea)A lot of these small creatures feed on the sea bed. THESAURUSthe sea especially British English the large area of salty water that covers much of the Earth’s surfaceShe lives by the sea.The sea was very rough.the ocean especially American English the large area of salty water that covers much of the Earth’s surfacea house by the oceanThe restaurant had a sweeping view of the ocean.waters a large area of water – used about an area of water that belongs to a particular country, or when describing what the water is likeboats fishing in Canadian watersBritish territorial watersthe calm waters of the harbourdangerous waterschoppy waters (=with a lot of waves)bay an area of sea that is partly enclosed by a curve in the landI swam across the bay.the Bay of Biscaygulf a very large area of sea partly enclosed by landthe Gulf of Mexicooil from the Gulf (=the area of water near Iran, Saudi Arabia etc)tide the regular rising and falling of the level of the seaIs the tide going out or coming in ?High tide (=when the sea is at its highest level)is at 4 o'clock in the afternoon.low tide (=when the sea is at its lowest level)The rocks are visible at low tide.wave a line of raised water that moves across the surface of the seaThe waves were crashing against the rocks.
Examples from the Corpussea• The war escalated, on the ground, in the air, and at sea.by the sea• Joe had discovered that at least twenty per cent of these water containers were gone, washed away by the sea.• Rex was captivated by the sea in a way that others might be avid golf players or inveterate bird watchers.• Our cottage lay on stubby cliffs close by the sea.• We bought a small cottage by the sea.• Eirias Park Spend your leisure time in Eirias Park - the park by the sea.• At Camasunary the bothy for walkers by the sea had a driftwood firelight glow coming through the window.• Long walks by the sea were needed to shake it all down and shake off the pounds that could so easily accumulate.• I find it very sad that the traditional weekend by the sea cam now be considered a health risk.