Part of grain provided for breakfast, perhaps (4)
I believe the answer is:
meal
I believe this is a double definition.
'part of grain' is the first definition.
(edible part of grain)
'for breakfast perhaps' is the second definition.
(breakfast is a kind of meal)
'provided' acts as a link.
(Other definitions for meal that I've seen before include "Powdered grain for dinner say" , "Scoff" , "Coarsely ground grain" , "Ground grain or pulses" , "Something to eat" .)