Seed of the cacao tree (5)
I believe the answer is:
cocoa
'seed of the cacao tree' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cocoa that I've seen before include "Powdered cacao seeds" , "Hot chocolate drink" , "Chocolate powder" , "Bedtime drink made from powder" , "Hot brown drink" .)