Head of bank with responsibility for extra money (5)
I believe the answer is:
bonus
'extra money' is the definition.
(I've seen this before)
'head of bank with responsibility' is the wordplay.
'head of' suggests taking the first letters.
'with' means one lot of letters go next to another.
'responsibility' becomes 'onus' (I've seen this before).
The initial letter of 'bank' is 'b'.
'b'+'onus'='BONUS'
'for' is the link.
(Other definitions for bonus that I've seen before include "Money on top of wages or salary" , "Extra payment, may be performance-related" , "Good-performance payment" , "Sum added to salary for good performance" , "Additional payment as reward for service" .)