--- victory, goal achieved at a ruinous cost (7)
I believe the answer is:
pyrrhic
(Other definitions for pyrrhic that I've seen before include "This kind of victory is too costly" , "Such a victory as bad as defeat" , "A victory won at such great cost that it's not a triumph" , "(Of victory) where winner's losses are as great as loser's" , "This victory comes at too great a price" .)