Food basic (6)
I believe the answer is:
staple
'food basic' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for staple that I've seen before include "Fasten with short U-shaped bits of wire" , "Paper fastener found on plates" , "Leading commodity" , "Basic commodity and paper fastener" , "Paper pin - basic" .)