Responsibility of bachelor abandoning extra benefit (4)
I believe the answer is:
onus
'responsibility' is the definition.
(onus is a duty or responsibility)
'bachelor abandoning extra benefit' is the wordplay.
'bachelor' becomes 'b' (abbreviation e.g. BA=Bachelor of Arts).
'abandoning' suggests deleting specific letters.
'extra benefit' becomes 'bonus'.
'bonus' with 'b' removed is 'ONUS'.
'of' acts as a link.
(Other definitions for onus that I've seen before include "'Burden, of proof (4)'" , "Obligation - charge" , "Responsibilty" , "Encumbrance" , "Liability" .)