1.NounA parliamentary rule in the Polish-Lithuanian Commonwealth, allowing any dissenting member of the legislature to force an immediate end to the current session and nullify any legislation that had already been passed.
2.NounAny system in which a single dissenting member can unilaterally block an action.
"The US, Russia, UK, France, and China have liberum veto power in the UN Security Council, allowing them to shield themselves and their allies from UN oversight."