Isthmian Games vs agon

Isthmian Games and agon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Isthmian Games	Yes	No	No	No
agon	Yes	No	No	No

As nouns, agon is a hypernym of Isthmian Games; that is, agon is a word with a broader meaning than Isthmian Games:

Isthmian Games: the ancient Panhellenic games held biennially on the Isthmus of Corinth in the first and third years of each Olympiad
agon: a festivity in ancient Greece at which competitors contended for prizes

Isthmian Games (noun)	agon (noun)
the ancient Panhellenic games held biennially on the Isthmus of Corinth in the first and third years of each Olympiad	a festivity in ancient Greece at which competitors contended for prizes