fountain vs geyser

fountain and geyser both are nouns.

Word	Noun	Adjective	Verb	Adverb
fountain	Yes	No	No	No
geyser	Yes	No	Yes	No

As nouns, geyser is a hyponym of fountain; that is, geyser is a word with a more specific, narrower meaning than fountain:

Other hyponyms of fountain include Fountain of Youth, hot spring, thermal spring.

fountain (noun)	geyser (noun)
a plumbing fixture that provides a flow of water	a spring that discharges hot water and steam
an artificially produced flow of water
a structure from which an artificially produced jet of water arises
a natural flow of ground water

fountain (verb)	geyser (verb)
	to overflow like a geyser