Extremely long time (4)
'extremely long time' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eon that I've seen before include "An immense time" , "Vast age; eternity" , "In time, long division" , "Age, epoch" , "thousand million years" .)
'extremely long time' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eons that I've seen before include "Long periods of time - noes have it" , "Times" , "Divisions of geological time" , "Divisions of archaeological time" , "Nose (anag)" .)