One of the Four Horsemen of the Apocalypse (3)
I believe the answer is:
war
'one of the four horsemen of the apocalypse' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for war that I've seen before include "State of armed conflict" , "Battle" , "Hostile situation" , "State of armed struggle" , "Large-scale conflict" .)