Horse, old joke (8)

I believe the answer is:

chestnut

I believe this clue is a double definition.

'horse' is the first definition.
(chestnut is a kind of horse)

'old joke' is the second definition.
(thesaurus)

(Other definitions for chestnut that I've seen before include "Dark golden-brown horse" , "Laughably predictable" , "Deep reddish-brown" , "''Underneath the spreading . . . . . . . . tree''" , "not a cracker!" .)

I've seen this clue in The Telegraph.

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