Supply a firearm part (5)
I believe the answer is:
stock
I believe this is a double definition.
'supply' is the first definition.
(stock can mean a supply or reserve)
'a firearm part' is the second definition.
(I know that stock is a type of firearm part)
(Other definitions for stock that I've seen before include "Equestrian tie" , "displaying little imagination?" , "Cravat worn as part of ridingkit" , "Broth" , "Supply; part of rifle" .)