The old coin is genuine (4)
I believe the answer is:
real
This might be a double definition.
'the old coin' is the first definition.
'real' can be an answer for 'coin' (real is a kind of coin). I'm not certain of the 'the old' bit.
'genuine' is the second definition.
(I know that genuine can be written as real)
'is' is the link.
Can you help me to learn more?
(Other definitions for real that I've seen before include "'Genuine, actual (4)'" , "Pukka" , "Not imaginary, genuine" , "Type of ale" , "Unaffected" .)