agon vs Isthmian Games

agon and Isthmian Games both are nouns.

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

As nouns, Isthmian Games is a hyponym of agon; that is, Isthmian Games is a word with a more specific, narrower meaning than agon:

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

Other hyponyms of agon include Nemean Games, Olympian Games, Olympic Games, Pythian Games.

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