Boss showing diligence discharging debts (4)
I believe the answer is:
stud
'boss' is the definition.
(both can mean a metal decoration)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for stud that I've seen before include "Boss; shirt fastener" , "Horse-breeding place" , "Collar-fastener" , "Ladies' man?" , "Collar fastener - form of poker" .)