Food; nail (4)
I believe the answer is:
tack
This clue is a double definition.
'food' is the first definition.
(I've seen this in other clues)
'nail' is the second definition.
(I know that tack is a type of nail)
(Other definitions for tack that I've seen before include "Nail - direction (eg of boat)" , "fix > riding gear" , "Poor food" , "Type of nail" , "Nail for carpet?" .)