Fruit seed radius (4)
I believe the answer is:
Here is my best explanation:
'fruit seed radius' is the definition.
'pear' can be an answer for 'fruit' (thesaurus). I am not sure about the 'seed radius' bit.
'fruit seed radius' is the subsidiary indication.
'fruit' becomes 'pea' (pea is a kind of fruit).
'seed radius' becomes 'r' (I am not sure about this - if you are sure you should believe this answer much more).
(Other definitions for pear that I've seen before include "Brand", "Avocado", "Tapering fleshy fruit - reap it", "Fruit related to apple", "Tasty fruit to reap", "Alternative to apple", "One fruit sounds like two", "Fruit; sounds like duo", "Pomaceous fruit" and "A fruit; sounds like couple".)