Eon, a variation of aeon, is defined as a unit of geological time equal to a billion years, or a very long period of time.(noun)
See eon in Webster's New World College Dictionary
Origin: LL < Gr aiōn, an age, lifetime, eternity < IE base *aiw-, vitality: see aye
See eon in American Heritage Dictionary 4
Origin: Late Latin aeōn
Origin: , from Greek aiōn; see aiw- in Indo-European roots.
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