Waste one's damaged cells (8)
I believe the answer is:
dungeons
'cells' is the definition.
(I know this)
'waste one's damaged' is the wordplay.
'waste' becomes 'dung' (dung is a kind of waste).
'damaged' indicates an anagram.
'ones' is an anagram of 'eons'.
'dung'+'eons'='DUNGEONS'
(Other definitions for dungeons that I've seen before include "Underground cells for prisoners" , "Underground prison cells" , "Underground prisons" .)