United Nations Abbr. UN An international organization composed of most of the countries of the world. It was founded in 1945 to promote peace, security, and economic development.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.United Nations n (functioning as singular or plural) 1. (Government, Politics & Diplomacy) an international organization of independent states, with its headquarters in New York City, that was formed in 1945 to promote peace and international cooperation and security. Abbreviation: UN 2. (Historical Terms) (in World War II) a coalition of 26 nations that signed a joint declaration in Jan 1942, pledging their full resources to defeating the Axis powers3. (Military) (in World War II) a coalition of 26 nations that signed a joint declaration in Jan 1942, pledging their full resources to defeating the Axis powersCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Unit?ed Na?tions n. 1. (used with a sing. v.) an international organization with headquarters in New York City, formed in 1945 to promote peace, security, and cooperation. Abbr.: UN, U.N. 2. (used with a pl. v.) the nations that signed a joint declaration in 1942, pledging to employ full resources against the Axis powers. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.