Money supply discovered, nothing missing (4)
I believe the answer is:
fund
'money supply' is the definition.
'discovered nothing missing' is the wordplay.
'discovered' becomes 'found' (finding is a kind of discovering).
'nothing' becomes 'o' (looks like zero - 0).
'missing' suggests deleting specific letters.
'found' with 'o' taken out is 'FUND'.
(Other definitions for fund that I've seen before include "Monetary resources" , "Stock of money available for particular purpose" , "Stock, resources" , "Give money" , "Cash reserve" .)