sea vs body of water

sea and body of water both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea	Yes	No	No	No
body of water	Yes	No	No	No

As nouns, body of water is a hypernym of sea; that is, body of water is a word with a broader meaning than sea:

sea: a division of an ocean or a large body of salt water partially enclosed by land
body of water: the part of the earth's surface covered with water (such as a river or lake or ocean)

Other hypernyms of sea include water.

sea (noun)	body of water (noun)
a division of an ocean or a large body of salt water partially enclosed by land	the part of the earth's surface covered with water (such as a river or lake or ocean)
turbulent water with swells of considerable size
anything apparently limitless in quantity or volume