Long, long times (4)
I believe the answer is:
'long long times' 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 "Divisions of geological time" , "Divisions of archaeological time" , "Years and years" , "Very long periods (US)" , "Long periods of time - noes have it" .)