Bar staple (3)
I believe the answer is:
rye
'bar staple' 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 "Hard liquor" , "J D Salinger novel 'The Catcher in the ...'" , "A Cinque Port; a grain" , "Grass - whiskey" , "Grass related to wheat" .)