amateur vs hobbyist

amateur and hobbyist both are nouns.

Word	Noun	Adjective	Verb	Adverb
amateur	Yes	Yes	No	No
hobbyist	Yes	No	No	No

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

Other hyponyms of amateur include bird watcher, birder, dabbler, dilettante, sciolist.

amateur (noun)	hobbyist (noun)
someone who pursues a study or sport as a pastime	a person who pursues an activity in their spare time for pleasure
an athlete who does not play for pay

amateur (adjective)	hobbyist (adjective)
engaged in as a pastime
lacking professional skill or expertise