Prepares for war (4)
I believe the answer is:
arms
'prepares for war' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arms that I've seen before include "Ordnance" , "Crest - guns" , "Equips for war" , "Protesting violently, up in these" , "military equipment" .)