Cocoa substitute (5)
I believe the answer is:
carob
'cocoa substitute' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for carob that I've seen before include "Bean, a choc. substitute" , "Arabian tree with brownish-purple pods" , "Chocolate substitute pod" , "St John's bread" , "Evergreen tree with edible pods" .)