Gold, sir, returns a fragrance (5)
I believe the answer is:
orris
'a fragrance' is the definition.
'gold sir returns' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'returns' is a reversal indicator.
'sir' backwards is 'ris'.
'or'+'ris'='ORRIS'
(Other definitions for orris that I've seen before include "Percussion instrument" , "Fragrant root used in perfumery" , "Iris with fragrant rhizome" , "Preparation" , "Type of flower" .)