Smart clothes beginning to lend one refinement (6)
I believe the answer is:
polish
'refinement' is the definition.
('polish' can be a synonym of 'refinement')
'smart clothes beginning to lend one' is the wordplay.
'smart' becomes 'posh' (I've seen this before**).
'clothes' is an insertion indicator.
'beginning to' says to take the initial letters.
'one' becomes 'i' (Roman numeral).
The first letter of 'lend' is 'l'.
'l'+'i'='li'
'posh' enclosing 'li' is 'POLISH'.
(Other definitions for polish that I've seen before include "Rub to make the surface shine" , "'Buff, burnish (6)'" , "Rub to a gloss" , "Europeans" , "See 1" .)