An authoritative prohibition or negative; a forbidding; an
interdiction.

A power or right possessed by one department of government to
forbid or prohibit the carrying out of projects attempted by another
department; especially, in a constitutional government, a power vested
in the chief executive to prevent the enactment of measures passed by
the legislature. Such a power may be absolute, as in the case of the
Tribunes of the People in ancient Rome, or limited, as in the case of
the President of the United States. Called also the veto power.

The exercise of such authority; an act of prohibition or
prevention; as, a veto is probable if the bill passes.

A document or message communicating the reasons of the
executive for not officially approving a proposed law; – called also
veto message.