Sure to fail (6)
I believe the answer is:
doomed
'sure to fail' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for doomed that I've seen before include "Destined to a grim fate, perhaps hell (6)" , "Damned or condemned" , "Condemned to destruction" , "Condemned to failure" , "Condemned to hell" .)