swimmer vs surfer

swimmer and surfer both are nouns.

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

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

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

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