Punish severely (7)
I believe the answer is:
scourge
'punish severely' is the definition.
(synonyms)
This is all the clue.
(Other definitions for scourge that I've seen before include "Affliction - whip" , "Whip; source of suffering" , "Punish severely" , "Whip; agent of suffering" , "Whip, flog" .)