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.