Gaudy trim, not new (6)
I believe the answer is:
garish
'gaudy' is the definition.
('garish' can be a synonym of 'gaudy')
'trim not new' is the wordplay.
'trim' becomes 'garnish' ('garnish' can be a synonym of 'trim').
'not' indicates named letters should be taken away.
'new' becomes 'n'.
'garnish' with 'n' taken out is 'GARISH'.
(Other definitions for garish that I've seen before include "Hag, sir, could be gaudy" , "Loud" , "Bright and showy" , "Vulgarly colourful" , "Tastelessly showy" .)