Bread for a Reuben sandwich
I believe the answer is:
rye
'bread for a reuben sandwich' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rye that I've seen before include "Burns's body came through" , "Bitterly regret" , "Gypsy gentleman" , "Kind of serial or American whiskey" , "Wheat-like cereal plant" .)