Real Dictionary

veto
verb: If someone in authority vetoes something, they forbid it, or stop it being put into action.

veto in American English
an order prohibiting some proposed or intended act; prohibition, esp. by a person in authority
to prevent (a bill) from becoming law by a veto
noun: the power or right vested in one branch of a government to cancel or postpone the decisions, enactments, etc., of another branch, esp. the right of a president, governor, or other chief executive to reject bills passed by the legislature

veto in British English
noun: the power to prevent legislation or action proposed by others; prohibition
verb: to refuse consent to (a proposal, esp a government bill)