Chestnut horse (6)
I believe the answer is:
sorrel
'chestnut horse' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sorrel that I've seen before include "Reddish brown horse or sharp-tasting herb" , "Light brown: salad leaf" , "It provides flavour" , "Light-chestnut horse" , "Edible plant, horse of light reddish-brown coat" .)