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.