veto

Short definition from Wiktionary

Noun

1. 1
   A political right to disapprove of (and thereby stop) the process of a decision, a law etc.
2. 2
   An invocation of that right.
3. 3
   An authoritative prohibition or negative; a forbidding; an interdiction.
4. 4
   A technique or mechanism for discarding what would otherwise constitute a false positive in a scientific experiment.

Verb

1. 1
   To use a veto against.
2. 2
   To countermand.