Fifth columnist's gold chasing characteristic (7)
I believe the answer is:
traitor
'fifth columnist's' is the definition.
(thesaurus)
'gold chasing characteristic' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'chasing' is a charade indicator (letters next to each other).
'characteristic' becomes 'trait' (I've seen this before).
'or' put after 'trait' is 'TRAITOR'.
(Other definitions for traitor that I've seen before include "Disloyal person" , "Renegade" , "Unreliable type" , "One committing treason" , "Betrayer, deceiver" .)