fountain vs plumbing fixture

fountain and plumbing fixture both are nouns.

Word	Noun	Adjective	Verb	Adverb
fountain	Yes	No	No	No
plumbing fixture	Yes	No	No	No

As nouns, plumbing fixture is a hypernym of fountain; that is, plumbing fixture is a word with a broader meaning than fountain:

fountain: a plumbing fixture that provides a flow of water
plumbing fixture: a fixture for the distribution and use of water in a building

fountain (noun)	plumbing fixture (noun)
a plumbing fixture that provides a flow of water	a fixture for the distribution and use of water in a building
an artificially produced flow of water
a structure from which an artificially produced jet of water arises
a natural flow of ground water