mountain vs volcano

mountain and volcano both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain	Yes	No	No	No
volcano	Yes	No	No	No

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

mountain: a land mass that projects well above its surroundings; higher than a hill
volcano: a mountain formed by volcanic material

Other hyponyms of mountain include alp, ben, seamount.

mountain (noun)	volcano (noun)
a land mass that projects well above its surroundings; higher than a hill	a mountain formed by volcanic material
(often followed by `of') a large number or amount or extent	a fissure in the earth's crust (or in the surface of some other planet) through which molten lava and gases erupt