Stone fruit aren't nice cut up (9)
I believe the answer is:
nectarine
'stone fruit' is the definition.
'nectarine' can be an answer for 'fruit' (nectarine is a kind of fruit). I'm unsure of the 'stone' bit.
'aren't nice cut up' is the wordplay.
'cut up' indicates an anagram.
'arent'+'nice'='arentnice'
'arentnice' with letters rearranged gives 'NECTARINE'.
Can you help me to learn more?
(Other definitions for nectarine that I've seen before include "fruity" , "Fruit - aren't nice (anag)" , "Smooth-skinned fruit" , "creating a sort of jam" , "Variety or mutation of a peach" .)