Wherein to keep money on the side (4)
I believe the answer is:
bank
This clue could be a double definition.
'wherein to keep money' is the first definition.
I know that 'money' relates to this answer.
'the side' is the second definition.
(bank is a kind of side)
'on' acts as a link.
Can you help me to learn more?
(Other definitions for bank that I've seen before include "Reserve" , "Row" , "area by river" , "Count" , "deposit" .)