Genuine old Spanish coin (4)
I believe the answer is:
real
This clue is a double definition.
'genuine' is the first definition.
(I know that genuine can be written as real)
'old spanish coin' is the second definition.
(former Spanish currency)
(Other definitions for real that I've seen before include "Spanish football team" , "---- Madrid, Spanish football club" , "Existing, not imaginery" , "Actual, not imagined" , "Actual, not illusory" .)