Destructive (7)
I believe the answer is:
ruinous
'destructive' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ruinous that I've seen before include "Calamitous, crippling" , "Exorbitant" , "Destructive; dilapidated" , "Causing destruction" , "ikely to cause harm" .)