W is for weapon (7)
I believe the answer is:
warhead
'w' is the definition.
(head of the word 'war')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for warhead that I've seen before include "bit of a weapon" , "Charge" , "Missile's explosive" , "Explosive missile part" , "Missile explosive unit" .)