The opposite of a fit banknoteA used banknote that the central bank deems fit to be returned into circulation. More. A banknoteA banknote (or ‘bill’ as it is often referred to in the US) is a type of negotiable promissory note, issued by a bank or other licensed authority, payable to the bearer on demand. More which, due to its deterioration or poor quality, is no longer suitable to be returned into circulation, and will be destroyed by the central bank.