Lo-o-ong time
I believe the answer is:
eon
'lo-o-ong 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 "Very long period (US and technical spelling)" , "Immense period" , "Long period of time" , "Huge time period" , "Prolonged period" .)