mountaineer vs adventurer

mountaineer and adventurer both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountaineer	Yes	No	Yes	No
adventurer	Yes	No	No	No

As nouns, adventurer is a hypernym of mountaineer; that is, adventurer is a word with a broader meaning than mountaineer:

Other hypernyms of mountaineer include venturer, climber.

mountaineer (noun)	adventurer (noun)
someone who climbs mountains	a person who enjoys taking risks
	someone who travels into little known regions (especially for some scientific purpose)

mountaineer (verb)	adventurer (verb)
climb mountains for pleasure as a sport