Eonian
ahd-5
adjective.
Of, relating to, or constituting an eon.
The Century Dictionary and Cyclopedia
Lasting for eons or ages; everlasting.
Wiktionary, Creative Commons Attribution/Share-Alike License
adjective.
Of or pertaining to an
eon
adjective.
everlasting
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adjective.
of or relating to a geological eon (longer than an era)
adjective.
continuing forever or indefinitely
Equivalent
lasting
permanent
suggests
eolian