Bank gives free change (4)
I believe the answer is:
reef
'bank' is the definition.
(I've seen this before)
'free change' is the wordplay.
'change' is an anagram indicator.
'free' with letters rearranged gives 'REEF'.
'gives' is the link.
(Other definitions for reef that I've seen before include "Ridge of rock underwater" , "Low-lying coral ridge" , "Chain of rocks near the surface of the sea" , "portion of sail" , "Great Barrier formation?" .)