swimmer vs diver

swimmer and diver both are nouns.

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

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

Other hyponyms of swimmer include backstroker, breaststroker, plunger, skinny-dipper.

swimmer (noun)	diver (noun)
a trained athlete who participates in swimming meets	large somewhat primitive fish-eating diving bird of the Northern Hemisphere having webbed feet placed far back; related to the grebes
a person who travels through the water by swimming	someone who dives (into water)
	someone who works underwater