Warlord keeps head from Trident weapon (7)
I believe the answer is:
shotgun
'weapon' is the definition.
(shotgun is a kind of weapon)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for shotgun that I've seen before include "Smooth-bore weapon" , "No thugs (anag) - weapon" , "Hunting firearm" , "arm" , "Type of wedding - weapon" .)