Waste long time in prisons (8)
I believe the answer is:
dungeons
'prisons' is the definition.
(I have seen 'Underground prisons' mean 'dungeons' so perhaps 'prisons' could also mean 'dungeons')
'waste long time' is the wordplay.
'waste' becomes 'dung' (dung is a kind of waste).
'long time' becomes 'eons' (I've seen this in another clue).
'dung'+'eons'='DUNGEONS'
'in' acts as a link.
(Other definitions for dungeons that I've seen before include "Underground prison cells" , "Underground cells for prisoners" , "Underground prisons" .)