Silver buck returned as decided (6)
I believe the answer is:
agreed
'decided' is the definition.
(agree can mean to settle or decide something)
'silver buck returned' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'buck' becomes 'deer' (buck can mean a male deer).
'returned' shows that the letters should be reversed in order.
'deer' reversed gives 'reed'.
'ag'+'reed'='AGREED'
'as' acts as a link.
(Other definitions for agreed that I've seen before include "Accepted; tallied" , "Accorded" , "Okayed" , "came to the same conclusion" , "Let's do it!" .)