Decided silver buck perhaps must be returned (6)
I believe the answer is:
agreed
'decided' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'silver buck perhaps must be returned' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'buck perhaps must be' becomes 'deer' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'returned' says the letters should be written backwards.
'deer' in reverse letter order is 'reed'.
'ag'+'reed'='AGREED'
Can you help me to learn more?
(Other definitions for agreed that I've seen before include "Jointly decided" , "Was fitting" , "'Concurred, assented (6)'" , "Of one mind" , "matched" .)