swimmer vs surfboarder

swimmer and surfboarder both are nouns.

Word	Noun	Adjective	Verb	Adverb
swimmer	Yes	No	No	No
surfboarder	Yes	No	No	No

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

Other hyponyms of swimmer include floater, aquanaut, skin-diver, surfer.

swimmer (noun)	surfboarder (noun)
a trained athlete who participates in swimming meets	someone who engages in surfboarding
a person who travels through the water by swimming