Former Italian banker seen in trade fair (4)
I believe the answer is:
expo
'trade fair' is the definition.
(I've seen this before)
'former italian banker' is the wordplay.
'former' becomes 'ex'.
'italian banker' becomes 'po' (Italian river, something that 'banks').
'ex'+'po'='EXPO'
'seen in' acts as a link.
(Other definitions for expo that I've seen before include "Public spectacle" , "public display" , "Public showing" , "Trade fair" , "Show" .)