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.-to prohibit; to negative; also, to refuse assent to, as a legislative bill, and thus prevent its enactment; as, to veto an appropriation bill.