Veto, a Latin word, signifying "I forbid," which has been introduced into the political language of modern nations to signify the act by which the executive power refuses its sanction to a measure proceeding from the legislature. The first instance of the use of this power was by the tribunes of the people in Rome, who, by pronouncing the word veto, could render of no avail the decrees of the senate or the proceedings of the magistrates. Under the ancient Polish constitution any single member of the diet, by the use of the liberum veto, saying Nie pozwalam (I do not allow), could hinder the passage of any measure. At the beginning of the French revolution the national assembly, in forming the constitution, allowed the king a conditional veto only; but the absolute veto was restored to the monarchy after the fall of Napoleon. The sovereign of England has theoretically a veto upon the measures of parliament, but it is a power which has not been used since 1707. In Norway the king has a veto; but if three successive storthings pass the same measure, it becomes a law in spite of the veto. In Sweden and the Netherlands the king has a full veto, and in other European countries there is an equivalent authority wherever the assent of the monarch is necessary to a law.

The president of the United States has a veto power, which has very frequently been exercised; but a majority of two thirds in each house of congress is sufficient to pass any measure over the veto. A similar conditional power over the acts of their respective legislatures is given to the governors of the several states, with the exception of Delaware, North Carolina, Ohio, Rhode Island, and West Virginia. In several of the states the veto may be overruled by a majority vote, but in most of them a majority of two thirds is required. Mayors of cities generally have a like power.