European banks to American (9)
I believe the answer is:
bostonian
'american' is the definition.
(I know that Bostonian is a type of american)
'european banks to' is the wordplay.
'european' becomes 'bosnian' (someone from Bosnia).
'banks' means one lot of letters goes inside another (bank can mean to surround or border).
'bosnian' enclosing 'to' is 'BOSTONIAN'.
(Other definitions for bostonian that I've seen before include "US state capitalist" , "US citizen" .)