body of water vs gulf

body of water and gulf both are nouns.

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

As nouns, gulf is a hyponym of body of water; that is, gulf is a word with a more specific, narrower meaning than body of water:

body of water: the part of the earth's surface covered with water (such as a river or lake or ocean)
gulf: an arm of a sea or ocean partly enclosed by land; larger than a bay

body of water (noun)	gulf (noun)
the part of the earth's surface covered with water (such as a river or lake or ocean)	an unbridgeable disparity (as from a failure of understanding)
	a deep wide chasm
	an arm of a sea or ocean partly enclosed by land; larger than a bay