Well-rounded fruit — apple core (5)
I believe the answer is:
plump
'well-rounded' is the definition.
(I've seen this in another clue)
'fruit apple core' is the wordplay.
'fruit' becomes 'plum' (plum is a kind of fruit).
'core' means to look at the middle letters.
The centre of 'apple' is 'p'.
'plum'+'p'='PLUMP'
(Other definitions for plump that I've seen before include "Well rounded - opt suddenly" , "Fat - set down unceremoniously" , "Not obese, just pleasantly rounded" , "Chubby, rounded" , "Rather fat" .)