Stale old joke involving golden-brown horse (8)
I believe the answer is:
chestnut
This clue is a quadruple definition!!
'stale old joke' is the first definition.
(an old chestnut is an old joke)
'involving' acts as a link.
'golden' is the second definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'brown' is the third definition.
(shade of brown)
'horse' is the fourth definition.
(I know that chestnut is a type of horse)
(Other definitions for chestnut that I've seen before include "Horse coat colour" , "Reddish-brown colour" , "Tree - reddish-brown" , "Old story" , "Laughably predictable" .)