Bank perhaps fine not opening? (6)
I believe the answer is:
lender
'not opening?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'bank perhaps fine' is the wordplay.
I cannot quite see how this works, but
'fine' could be 'end' (I've seen this before) and 'end' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for lender that I've seen before include "Provider of a loan" , "Syrup-yielding tree" , "One gives credit" , "Neither a borrower nor a ... be, it's said" , "He makes a loan" .)