Ledger entry’s extremely defective part (5)
I believe the answer is:
debit
'ledger entry's' is the definition.
(debit is a kind of ledger entry)
'extremely defective part' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'part' becomes 'bit' (both mean a piece of something).
'defective' with its middle removed is 'de'.
'de'+'bit'='DEBIT'
(Other definitions for debit that I've seen before include "Opposite of 23 across" , "Accounting entry showing sum owing" , "Money owed" , "Accounting entry showing sums owing" , "Sum removed from a bank account" .)