Portending evil (7)
I believe the answer is:
ominous
'portending evil' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ominous that I've seen before include "Portending bad things" , "Menacing, sinister" , "'Sinister, baleful (7)'" , "Minatory, trouble coming" , "Portentous" .)