Trade using former coins (8)
I believe the answer is:
exchange
'trade' is the definition.
(exchange of items)
'former coins' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'coins' becomes 'change' (change can mean coins).
'ex'+'change'='EXCHANGE'
'using' is the link.
(Other definitions for exchange that I've seen before include "Swap, barter" , "Altercation" , "truck" , "Short conversation or argument" , "place of business" .)