Oval fruit (4)
'oval fruit' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for plum that I've seen before include "Prize" , "murderer" , "Brilliant" , "Fruit < that's highly desirable" , "Fruit; something choice" .)
(Other definitions for olive that I've seen before include "Source of edible oil" , "I love this fruit" , "This branch is offered in peace gesture" , "woman" , "One's stoned" .)