See Pat exchanging former currency (6)
I believe the answer is:
peseta
'former currency' is the definition.
(I've seen this before)
'see pat exchanging' is the wordplay.
'exchanging' indicates an anagram (I've seen 'exchange' mean this).
'see'+'pat'='seepat'
'seepat' anagrammed gives 'PESETA'.
(Other definitions for peseta that I've seen before include "Former Spanish monetary unit" , "Domestic social" , "Pre-euro money unit in Spain" , "Former monetary unit of Spain" , "Obsolete coin" .)