Almost round purple fruit (4)
I believe the answer is:
plum
'purple fruit' is the definition.
(plums can be purple)
'almost round' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'round' becomes 'plump' (both can mean fat or chubby).
'plump' with its final letter removed is 'PLUM'.
(Other definitions for plum that I've seen before include "Best; fruit" , "superior kind?" , "Fruit < that's highly desirable" , "Purple fruit" , "Oval fruit with single hard stone" .)