Outfit including new jewellery (4)
I believe the answer is:
ring
'jewellery' is the definition.
(ring is a kind of jewellery)
'outfit including new' is the wordplay.
'outfit' becomes 'rig' ('rig' can be a synonym of 'outfit'**).
'including' means one lot of letters goes inside another.
'new' becomes 'n'.
'rig' going around 'n' is 'RING'.
(Other definitions for ring that I've seen before include "Circular object - sound" , "Contact" , "Group of criminals maybe" , "Besiegers' formation" , "Group operating illegally < call" .)