Old coins a genius circulated (7)
I believe the answer is:
guineas
'old coins' is the definition.
'guineas' can be an answer for 'coins' (guinea is a kind of coin). I am not certain of the 'old' bit.
'a genius circulated' is the wordplay.
'circulated' indicates anagramming the letters.
'a'+'genius'='agenius'
'agenius' with letters rearranged gives 'GUINEAS'.
Can you help me to learn more?
(Other definitions for guineas that I've seen before include "Old money - run at Newmarket" , "Obsolete coins (still used at Newmarket?)" , "Former gold coins" , "They used to be worth 21 shillings" .)