Greek character in bank, by the sound of it? (3)
I believe the answer is:
rho
'greek character' is the definition.
(letter from the Greek alphabet)
'bank by the sound of it?' is the wordplay.
'bank' becomes 'row' (a bank is a row of things).
'by the sound of it?' shows a homophone (sound like).
'row' is a homophone of 'RHO'.
'in' is the link.
(Other definitions for rho that I've seen before include "Seventeenth letter of the Greek alphabet" , "Greek letter R" , "Sophocles character" , "Gr. letter written as P" , "Greek P" .)