Charge one for being in debt (5)
I believe the answer is:
debit
'charge' is the definition.
(I know that charge is a more specific form of the action debit)
'one for being in debt' is the wordplay.
'one' becomes 'i' (Roman numeral).
'for being in' indicates putting letters inside.
'i' put into 'debt' is 'DEBIT'.
(Other definitions for debit that I've seen before include "Accounting entry showing amount spent" , "Accounting entry recording sums that are 5" , "It's not to one's credit" , "Deduct from account" , "Sum removed from a bank account" .)