Further returns in private bank (4)
I believe the answer is:
abet
'further' is the definition.
(thesaurus)
'returns in private bank' is the wordplay.
'returns' says the letters should be written in reverse.
'in' indicates the answer is hidden within the clue.
'teba' is hidden in the letters of 'private bank'.
'teba' back-to-front is 'ABET'.
(Other definitions for abet that I've seen before include "Criminally endorse" , "Give aid to" , "Encourage (offence)" , "Incite, help" , "Egg on" .)