Chocolate substitute (5)
I believe the answer is:
carob
'chocolate substitute' is the definition.
(carob powder is a chocolate substitute)
This is the entire clue.
(Other definitions for carob that I've seen before include "Bean, a choc. substitute" , "Saint John's bread" , "Evergreen tree with edible pods" , "St John's bread" , "Arabian tree with brownish-purple pods" .)