Portending tragedy (7)
I believe the answer is:
ominous
'portending tragedy' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ominous that I've seen before include "Menacing, sinister" , "US moon I find threatening" , "Threatening, foreshadowing something bad" , "Inauspicious" , "Foreboding, menacing" .)