Old weapon (7)
(Other definitions for blunderbuss that I've seen before include "old handgun" , "Early form of gun" , "Clumsy person" , "one was fired" , "Old musket" .)
(Other definitions for longbow that I've seen before include "Decisive weapon at Agincourt" , "Weapon shooting arrows" , "Medieval weapon" , "taken up by The Archers" , "Powerful wooden weapon used against the French at Agincourt" .)
'old weapon' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for halberd that I've seen before include "Old weapon" , "Ancient battle-axe" , "Ancient weapon" , "Combined spear and battleaxe" , "Sharp instrument" .)