Smarter bit of couture: it tantalises when twirling (7)
I believe the answer is:
nattier
'smarter' is the definition.
(natty can mean smart or stylish)
'bit of couture it tantalises when twirling' is the wordplay.
'bit of' indicates a hidden word.
'twirling' shows that the letters should be reversed in order.
'reittan' is hidden in the letters of 'couture it tantalises when'.
'reittan' in reverse letter order is 'NATTIER'.
(Other definitions for nattier that I've seen before include "Like the smarter set" , "Smarter and more fashionable" , "less scruffy" , "Louis XV court painter; more dapper" , "More clever" .)