Impatient for silver to go back (4)
I believe the answer is:
agog
'impatient' is the definition.
(I've seen this before)
'silver to go back' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'to' means one lot of letters go next to another.
'back' says the letters should be written backwards.
'go' backwards is 'og'.
'ag'+'og'='AGOG'
'for' acts as a link.
(Other definitions for agog that I've seen before include "Eager - in suspense" , "Eager or curious" , "Eagerly excited" , "Full of expectation" , "Eager, avid" .)