Second promise to produce weapon (5)
I believe the answer is:
sword
'weapon' is the definition.
(sword is a kind of weapon)
'second promise' is the wordplay.
'second' becomes 's' (common abbreviation).
'promise' becomes 'word' (as in 'I give you my word').
's'+'word'='SWORD'
'to produce' is the link.
(Other definitions for sword that I've seen before include "Command; social class" , "Combat" , "used for fencing" , "Long-bladed weapon" , "Sharp-edged weapon" .)