Amount to be divided (3)
I believe the answer is:
'amount to be divided' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pie that I've seen before include "In the sky, it's a hopeless idea" , "A baked dish covered with pastry" , "steak might go in this" , "Fruit or meat dish" , "something with custard, say" .)