eternal vs eonian

eternal and eonian both are adjectives.

Word	Noun	Adjective	Verb	Adverb
eternal	No	Yes	No	No
eonian	No	Yes	No	No

As adjectives, eternal and eonian are synonyms defined as:

Other synonyms of eternal include aeonian, ageless, everlasting, perpetual, unceasing, unending.

eternal (adjective)	eonian (adjective)
tiresomely long; seemingly without end	of or relating to a geological eon (longer than an era)
continuing forever or indefinitely	continuing forever or indefinitely