Traded in old coins and pennies (9)
I believe the answer is:
exchanged
'traded in' is the definition.
The answer and definition can be both to do with ownership as well as being past participle verbs.
Perhaps they are linked in a way I don't understand?
'old coins and pennies' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'coins' becomes 'change' (change can mean coins).
'and' means one lot of letters go next to another.
'pennies' becomes 'd' (abbreviation e.g. Lsd - pounds, shillings, pence).
'ex'+'change'+'d'='EXCHANGED'
Can you help me to learn more?
(Another definition for exchanged that I've seen is " Swapped".)