American notes that have been in circulation (4)
I believe the answer is:
used
'american notes that have been in circulation' is the definition.
Although both the answer and definition are adjectives, I can't see how one could define the other.
'american notes' is the wordplay.
'american' becomes 'us' (abbreviation for United States).
'notes' becomes 'ed'.
'us'+'ed'='USED'
Can you help me to learn more?
(Other definitions for used that I've seen before include "Second-hand, not new" , "Scottish expert" , "took a chance on becoming dependent" , "That's not new" , "given employment" .)