Bum touring new French city (6)
I believe the answer is:
nantes
'french city' is the definition.
(I've seen this in another clue)
'bum touring new' is the wordplay.
'bum' becomes 'nates' (anatomical term for the buttocks).
'touring' means one lot of letters goes inside another (touring can mean going round).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'nates' enclosing 'n' is 'NANTES'.
(Other definitions for nantes that I've seen before include "Loire port; an old Edict" , "City on the Loire, associated with 1598 edict ending the French Wars of Religion" , "Western French port" , "French FC" , "City in Brittany" .)