Horse, an old joke (8)
I believe the answer is:
chestnut
I believe this is a double definition.
'horse' is the first definition.
(I know that chestnut is a type of horse)
'an old joke' is the second definition.
(as in an old chestnut)
(Other definitions for chestnut that I've seen before include "Golden to reddish brown colour" , "Wooden" , "comedian's overused line?" , "Item for stuffing" , "Dark golden-brown horse" .)