winner vs medallist

winner and medallist both are nouns.

Word	Noun	Adjective	Verb	Adverb
winner	Yes	No	No	No
medallist	Yes	No	No	No

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

Other hyponyms of winner include contestee, medalist, upsetter, walloper.

winner (noun)	medallist (noun)
the contestant who wins the contest	(golf) the winner at medal play of a tournament
a gambler who wins a bet	someone who has won a medal
a person with a record of successes