Forbid free bread (5)
I believe the answer is:
debar
'forbid' is the definition.
(debarring is a kind of forbiding)
'free bread' is the wordplay.
'free' indicates an anagram.
'bread' anagrammed gives 'DEBAR'.
(Other definitions for debar that I've seen before include "Blackball" , "Large advert" , "Stop" , "Exclude - bread (anag)" , "Exclude (from right)" .)