Second article in gold (5)
I believe the answer is:
other
'second' is the definition.
(I've seen this before)
'article in gold' is the wordplay.
'article' becomes 'the' (the definite article).
'in' is an insertion indicator.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'the' inserted inside 'or' is 'OTHER'.
(Other definitions for other that I've seen before include "Throe (anag)" , "Alternate; additional" , "Different (from those mentioned)" , "Alternative of two" , "Second" .)