Family name of Swiss banker taken in by scam (8)
I believe the answer is:
cognomen
'family name' is the definition.
(synonyms)
'swiss banker taken in by scam' is the wordplay.
'swiss banker' becomes 'gnome' (informal term for a banker, esp. one in Zurich).
'taken in by' is an insertion indicator.
'scam' becomes 'con' (I've seen this before).
'gnome' put into 'con' is 'COGNOMEN'.
'of' is the link.
(Other definitions for cognomen that I've seen before include "Epithet" , "Family name" , "Nickname -- eg non-com (anag)" , "Con gnome using kind of nickname" .)