Boss in poker game (4)
I believe the answer is:
stud
I believe this is a double definition.
'boss' is the first definition.
(both can mean a metal decoration)
'poker game' is the second definition.
(stud is a kind of poker game)
'in' acts as a link.
(Other definitions for stud that I've seen before include "Collar fastener or horse farm" , "Style of poker" , "virile fellow" , "sort of stable" , "Football boot attachment" .)