Adonis is boss (4)
I believe the answer is:
stud
This clue is a double definition.
'adonis' is the first definition.
(both can mean an attractive man)
'is boss' is the second definition.
(both can mean a metal decoration)
(Other definitions for stud that I've seen before include "Bejewel" , "Collar fastener or horse farm" , "Collar-fastener" , "Horse-breeding establishment; jewellery item" , "Small rounded earring" .)