Choose gold constituent (7)
I believe the answer is:
elector
'constituent' is the definition.
(synonyms)
'choose gold' is the wordplay.
'choose' becomes 'elect' (electing is a kind of choosing).
'gold' becomes 'or' ('or' is the heraldic name for gold).
'elect'+'or'='ELECTOR'
(Other definitions for elector that I've seen before include "One entitled to vote" , "One exercising suffrage" , "A prince of the Holy Roman Empire" , "one with a voice" , "One with the power to cross" .)