international organization founded in 1945 to promote peace security and international cooperation and promote humanitarianism (has its headquarters in New York City, USA)
The UN is the same as the United Nations. a UN peacekeeping mission. United Nations. good 'un/bad 'un/little 'un etc a short form of 'one', used to say that someone or something is good, bad etc. Teachers and careful speakers of English do not use this expression