Practically forever (5)
(Other definitions for aeons that I've seen before include "Vast ages" , "Long periods of time" .)
'practically forever' 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 "Geological period" , "Immense period" , "In time, long division" , "Vast period" , "An immense time" .)