mountain vs seamount

mountain and seamount both are nouns.

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

As nouns, seamount is a hyponym of mountain; that is, seamount 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
seamount: an underwater mountain rising above the ocean floor

Other hyponyms of mountain include alp, ben, volcano.

mountain (noun)	seamount (noun)
a land mass that projects well above its surroundings; higher than a hill	an underwater mountain rising above the ocean floor
(often followed by `of') a large number or amount or extent