A lo-o-ong time (4)
I believe the answer is:
eons
'a lo-o-ong 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 "Years and years" , "Divisions of archaeological time" , "Divisions of geological time" , "Very long periods (US)" , "Nose (anag)" .)