Banks of nowhere returned good gains for savings (4,3)
I believe the answer is:
nest egg
'savings' is the definition.
(synonyms)
'banks of nowhere returned good gains' is the wordplay.
'banks of' says to hollow out the word (remove centre letters) (the banks are the sides of the word).
'returned' shows that the letters should be reversed in order.
'good' becomes 'g' (abbreviation).
'gains' becomes 'gets'.
'nowhere' with its centre taken out is 'ne'.
'g'+'gets'='ggets'
'ggets' written backwards gives 'stegg'.
'ne'+'stegg'='NEST-EGG'
'for' is the link.
(Other definitions for nest egg that I've seen before include "Savings for the future" , "Fund for a rainy day" , "Sum of money put by as a reserve" , "Sum of money saved, as bird would" , "a little money?" .)