estuary vs body of water

estuary and body of water both are nouns.

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

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

estuary: the wide part of a river where it nears the sea; fresh and salt water mix
body of water: the part of the earth's surface covered with water (such as a river or lake or ocean)

Other hypernyms of estuary include water.

estuary (noun)	body of water (noun)
the wide part of a river where it nears the sea; fresh and salt water mix	the part of the earth's surface covered with water (such as a river or lake or ocean)