Cover article in duplicate (6)
I believe the answer is:
canopy
'cover' is the definition.
(I know that canopy is a type of cover)
'article in duplicate' is the wordplay.
'article' becomes 'an' (indefinite article).
'in' indicates putting letters inside.
'duplicate' becomes 'copy' (I've seen this before).
'an' inserted within 'copy' is 'CANOPY'.
(Other definitions for canopy that I've seen before include "in the topmost branches" , "Covering against sun or rain" , "Uppermost branches of forest trees" , "Hanging cover forming shelter over bed or throne" , "Cloth covering" .)