Cause of great suffering (7)
I believe the answer is:
scourge
'cause of great suffering' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for scourge that I've seen before include "Cause great suffering to (someone); whip" , "administer punishment" , "Flog, punish" , "Cause of great affliction" , "Curse; whip" .)