Very long period (3)
'very long period' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for eon that I've seen before include "Long period of time" , "Vast period" , "In time, long division" , "An immense time" , "thousand million years" .)
'very long period' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for aeon that I've seen before include "Eternity" , "An immense period of time" , "Indefinitely long period of time" , "A very long time, an age" , "long term" .)