years vs eon

years and eon both are nouns.

Word	Noun	Adjective	Verb	Adverb
years	Yes	No	No	No
eon	Yes	No	No	No

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

Other hyponyms of years include month of Sundays, aeon, blue moon, year dot.

years (noun)	eon (noun)
a late time of life	(Gnosticism) a divine power or nature emanating from the Supreme Being and playing various roles in the operation of the universe
a prolonged period of time	an immeasurably long period of time
the time during which someone's life continues	the longest division of geological time