I. noun
or eon ˈēən, ˈēˌän
( -s )
Etymology: Latin aeon, from Greek aiōn age, lifetime — more at aye
1. : an immeasurably or indefinitely long period of time : age
the obscure aeons of prehistory
2. in Gnosticism especially as taught by the Valentinians : one of the group of eternal beings that together form the fullness of the supreme being from whom they emanate and between whom and the world they are intermediaries
3. usually eon : any large part of geological time usually longer than an era
Synonyms: see period
II. noun
: a unit of geologic time equal to one billion years