Ultimate in smart town headgear (6)
I believe the answer is:
turban
'headgear' is the definition.
(I know that turban is a type of headgear)
'ultimate in smart town' is the wordplay.
'ultimate in' indicates one should take the final letters.
'town' becomes 'urban' (urban means relating to a town or city).
The last letter of 'smart' is 't'.
't'+'urban'='TURBAN'
(Other definitions for turban that I've seen before include "Swathe of material as headdress" , "Sikh headgear" , "Wound headgear" , "But ran out for the headdress" , "Head-dress of male Muslim and Sikh" .)