a committee in the executive branch of government that advises the president on foreign and military and national security; supervises the Central Intelligence Agency
a powerful government committee in the US, which controls the relationship between military and foreign policy. Its members include the President, the Secretary of State, and the Defense Secretary, and its leader is the President's 'National Security Adviser'.
the most powerful part of the UNITED NATIONS, which is responsible for making sure that countries behave peacefully towards each other, and for deciding what the UNITED NATIONS should do if countries go to war. It is a committee of five permanent members (the US, the UK, Russia, France, and China) and ten other members who change every two years.