Countless years (3)
'countless years' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eon that I've seen before include "Vast age; eternity" , "Very long period (US and technical spelling)" , "Vast period" , "An immense time" , "Vast age (alt. sp.)" .)
'countless years' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eons that I've seen before include "Vast ages" , "Very long periods (US)" , "Years and years" , "Nose (anag)" , "Divisions of archaeological time" .)