Crustacean programme mostly bearing fruit (4,5)
I believe the answer is:
crab apple
'fruit' is the definition.
(crab apple is a kind of fruit)
'crustacean programme mostly bearing' is the wordplay.
'crustacean' becomes 'crab' (crab is a kind of crustacean).
'programme mostly' becomes 'appl' (I am not sure about this - if you are sure you should believe this answer much more).
'bearing' becomes 'e' (East, a compass bearing or direction).
'crab'+'appl'+'e'='CRAB-APPLE'
Can you help me to learn more?
(Other definitions for crab apple that I've seen before include "Small sour version of common orchard fruit" , "unappetizing fruit" , "Fruit tree with sour bright red crop" , "Tree bearing fruit for jelly" , "Tart fruit for making jam and jelly" .)