Carve in sweet chestnut (4)
I believe the answer is:
etch
'carve' is the definition.
(I've seen this before)
'in sweet chestnut' is the wordplay.
'in' says the answer is hidden in the clue.
'ETCH' can be found hidden inside 'sweet chestnut'.
(Other definitions for etch that I've seen before include "Cut; engrave" , "Score deeply" , "Cut deeply (with acid?)" , "Make carvings" , "Delineate" .)