A crooked sort in Swiss banker, bon vivant (10)
I believe the answer is:
gastronome
'bon vivant' is the definition.
(synonyms)
'a crooked sort in swiss banker' is the wordplay.
'crooked' is an anagram indicator (a crooked or disrupted version of the letters).
'in' means one lot of letters goes inside another.
'swiss banker' becomes 'gnome' (informal term for a banker, esp. one in Zurich).
'sort' is an anagram of 'stro'.
'a'+'stro'='astro'
'astro' placed within 'gnome' is 'GASTRONOME'.
(Other definitions for gastronome that I've seen before include "One who loves to eat" , "does he expect special fare?" , "foodie" , "Epicurean" .)