Covering article in duplicate (6)
I believe the answer is:
canopy
'covering' is the definition.
(canopy is a kind of covering)
'article in duplicate' is the wordplay.
'article' becomes 'an' (indefinite article).
'in' is an insertion indicator.
'duplicate' becomes 'copy' (I've seen this before).
'an' inserted inside 'copy' is 'CANOPY'.
(Other definitions for canopy that I've seen before include "Uppermost branches of forest trees" , "Cover above four-poster" , "Cockpit cover" , "Awning - roofed structure" , "Hanging cover forming shelter over bed or throne" .)