Cloak is carbon copy (4)
I believe the answer is:
cape
'cloak' is the definition.
(I know that cape is a type of cloak)
'carbon copy' is the wordplay.
'carbon' becomes 'C' (C is the chemical symbol for carbon).
'copy' becomes 'ape' (ape can mean to copy or imitate).
'c'+'ape'='CAPE'
'is' acts as a link.
(Other definitions for cape that I've seen before include "Point of land jutting out into the water" , "Wrath, say" , "Short sleeveless garment" , "Cod, for example" , "Loose cloak or promontory" .)