See Pat exchanging foreign currency (6)
I believe the answer is:
peseta
'foreign currency' is the definition.
'peseta' can be an answer for 'currency' (I have seen 'Spanish currency' mean 'peseta' so perhaps 'currency' could also mean 'peseta'). I am unsure of the 'foreign' bit.
'see pat exchanging' is the wordplay.
'exchanging' is an anagram indicator (I've seen 'exchanged' mean this).
'see'+'pat'='seepat'
'seepat' anagrammed gives 'PESETA'.
Can you help me to learn more?
(Other definitions for peseta that I've seen before include "once tender elsewhere" , "Former Spanish monetary unit" , "Previous Spanish money unit" , "Spanish coinage" , "little cash is required" .)