eon

the word 'eon' entered english in the 17th century via latin 'aeon', which was borrowed from the greek 'aiṓn', meaning 'age', 'lifetime', or 'eternity'. in ancient greek philosophy and gnostic thought, 'aiṓn' took on profound metaphysical connotations, referring to eternal beings or boundless periods of cosmic time. this sense of a vast, immeasurable span was carried into modern scientific and general english, where it denotes either an indefinitely long age or a specific, major division of geological chronology.

the word is a simplex loanword from latin, ultimately from greek. it is not productively formed from separable morphemes in modern english.