Advance sterling on a possibility (4)
I believe the answer is:
loan
'advance sterling on a possibility' is the definition.
'loan' can be an answer for 'advance' (I've seen this before). I am unsure of the 'sterling on a possibility' bit.
'advance sterling on a' is the wordplay.
'advance sterling' becomes 'l' (I am not sure about the 'advance' bit.).
'on' becomes 'o' (I've seen this in other clues).
'a' becomes 'an'.
'l'+'o'+'an'='LOAN'
Can you help me to learn more?
(Other definitions for loan that I've seen before include "Credit" , "Advance (money)" , "Overdraft" , "Advance, borrowing" , "Act of lending" .)