sea 
/ˈsi:/ noun
plural seas /ˈsi:/ noun 1 a : the salt water that covers much of the Earth's surface [noncount] ▪ We traveled by sea. [=on a ship] — often used with the ▪ The ship sank to the bottom of the sea. [=the ocean] ▪ creatures of the sea ▪ He was sailing the open sea. [=sailing far away from land] — often used before another noun ▪ a sea voyage ▪ a sea animal/creature ▪ the sea floor [plural] (literary) ▪ the uncharted seas — see also high seas
b or Sea [count] : a large body of water that is part of the sea or that has land around part or all of it
▪ the Mediterranean Sea ▪ the seas of the Southern Hemisphere — see color picture; see also seven seas 2 [count] : an area of the sea — used to describe the movement of the water in the sea ▪ a calm/rough sea — often plural ▪ We sailed in heavy seas. [=in very large waves] 3 [count] : a large amount or number of people or things spread over a large area — usually singular ▪ a sea of screaming fans ▪ a golden sea of wheat — sometimes used figuratively ▪ a sea of sadness 4 or Sea [count] technical : one of the large, flat areas on the moon or on Mars
▪ lunar seas ▪ the Sea of Tranquility
b or Sea [count] : a large body of water that is part of the sea or that has land around part or all of it
▪ the Mediterranean Sea ▪ the seas of the Southern Hemisphere — see color picture; see also seven seas
▪ lunar seas ▪ the Sea of Tranquility
at sea 1 : sailing or traveling on the sea
▪ The navy spent as much time in port as they did at sea. ▪ The crew was lost at sea. [=the crew disappeared while traveling on the sea] 2 : confused and not confident
▪ She felt completely at sea when she started her new job.
▪ The navy spent as much time in port as they did at sea. ▪ The crew was lost at sea. [=the crew disappeared while traveling on the sea]
▪ She felt completely at sea when she started her new job.
between the devil and the deep blue sea — see devil
fish in the sea — see 1fish
go to sea
somewhat old-fashioned : to become a sailor
▪ He went to sea at a young age.
▪ He went to sea at a young age.
out to sea
: toward or into a part of the ocean that is far away from land
▪ The boat headed out to sea. ▪ He fell overboard and was swept out to sea.
▪ The boat headed out to sea. ▪ He fell overboard and was swept out to sea.
put (out) to sea
: to leave a port, harbor, etc., and begin traveling on the sea
▪ The ship put to sea. ▪ We will dock tonight and put out to sea tomorrow.
▪ The ship put to sea. ▪ We will dock tonight and put out to sea tomorrow.
