No longer usable (6)
I believe the answer is:
ruined
'no longer usable' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ruined that I've seen before include "Devastated" , "Reduced to a state of poverty" , "Destroyed or bankrupted" , "Utterly destroyed" , "Destroyed, undone" .)