athlete vs runner

athlete and runner both are nouns.

Word	Noun	Adjective	Verb	Adverb
athlete	Yes	No	No	No
runner	Yes	No	No	No

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

athlete (noun)	runner (noun)
a person trained to compete in sports	fish of western Atlantic: Cape Cod to Brazil
	device consisting of the parts on which something can slide along
	a long narrow carpet
	a trained athlete who competes in foot races
	someone who imports or exports without paying duties
	a baseball player on the team at bat who is on base (or attempting to reach a base)
	someone who travels on foot by running
	a person who is employed to deliver messages or documents
	(football) the player who is carrying (and trying to advance) the ball on an offensive play
	a horizontal branch from the base of plant that produces new plants from buds at its tips