Kill, as a bill (4)
I believe the answer is:
veto
'kill as a bill' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for veto that I've seen before include "Literally, 'I forbid'" , "Forbid outright" , "Right to reject a proposal" , "The power to prohibit or reject a proposal" , "Forbid; prohibition" .)