Disallow (4)
'disallow' is the definition.
(I know that disallow can be written as veto)
This is all the clue.
(Other definitions for veto that I've seen before include "bar" , "Stop" , "Red light" , "Rule out" , "The power to prohibit or reject a proposal" .)
'disallow' is the definition.
(I know that disallow can be written as nix)
This is the entire clue.
(Other definitions for nix that I've seen before include "Spiteful water spirit" , "Nothing (sl.)" , "0" , "Cancel" , "water sprite" .)