Bread grain (3)
I believe the answer is:
rye
'bread grain' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rye that I've seen before include "Whiskey (US)" , "Cereal plant; whisky" , "Hardy cereal crop" , "Cereal grass - Sussex Cinque Port" , "place in East Sussex" .)