Olympian vs athlete

Olympian and athlete both are nouns.

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

As nouns, athlete is a hypernym of Olympian; that is, athlete is a word with a broader meaning than Olympian:

Other hypernyms of Olympian include jock.

Olympian (noun)	athlete (noun)
an athlete who participates in the Olympic games	a person trained to compete in sports
a classical Greek god after the overthrow of the Titans

Olympian (adjective)	athlete (adjective)
of or pertaining to the greater gods of ancient Greece whose abode was Mount Olympus
of the region of Olympia in Greece or its inhabitants