foot race vs marathon

foot race and marathon both are nouns.

Word	Noun	Adjective	Verb	Adverb
foot race	Yes	No	No	No
marathon	Yes	No	No	No

As nouns, marathon is a hyponym of foot race; that is, marathon is a word with a more specific, narrower meaning than foot race:

Other hyponyms of foot race include fun run, funrun, obstacle race, steeplechase, track event.

foot race (noun)	marathon (noun)
a race run on foot	any long and arduous undertaking
	a footrace of 26 miles 385 yards