Ban, disallow (4)
I believe the answer is:
veto
I believe this is a double definition.
'ban' is the first definition.
(veto can mean a ban or prohibition on something)
'disallow' is the second definition.
(I know that disallow can be written as veto)
(Other definitions for veto that I've seen before include "Refuse permission" , "Embargo" , "Throw out" , "Ban; refuse to allow" , "Refuse to endorse" .)