It's a chip, twisted round a nut (9)
I believe the answer is:
pistachio
'a nut' is the definition.
(I know that pistachio is a nut)
'it's a chip twisted round' is the wordplay.
'twisted' indicates anagramming the letters.
'round' becomes 'o' (round can mean a round object).
'its'+'a'+'chip'='itsachip'
'itsachip' anagrammed gives 'pistachi'.
'pistachi'+'o'='PISTACHIO'
(Other definitions for pistachio that I've seen before include "Green nut" , "nut-bearing tree" , "Nut - it is a chop (anag)" , "Edible nut" , "Greenish nut" .)