Excellent joint objective discussed upfront (6)
I believe the answer is:
golden
'excellent' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for golden that I've seen before include "Most favourable; bright" , "- - handshake" , "50th Jubilee" , "Autumnal flower" , "- - wedding (50th)" .)