Corned beef sandwich bread (3)
I believe the answer is:
rye
'corned beef sandwich bread' 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 "Wheat-like cereal plant" , "Cereal used for making whiskey" , "American whisky" , "One of Cinque Ports" , "Hardy annual cereal grass" .)