Separate article is covered in gold (5)
I believe the answer is:
other
'separate' is the definition.
(associated in meaning)
'article is covered in gold' is the wordplay.
'article' becomes 'the' (the definite article).
'is covered in' is an insertion indicator.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'the' placed inside 'or' is 'OTHER'.
(Other definitions for other that I've seen before include "Not the one mentioned" , "Distinct" , "Different (from those mentioned)" , "Different; alternate" , "Alternate; additional" .)