This book is published by the government of New Zealand, and it is an excellent reference source on the United Nations. It is updated annually and provides an excellent index for the ongoing work if the U.S.
Us this site to search for any word, and it will give you the UN's official rendition. This will also give you excellent style notes on demonyms and what the official UN short names are for different countries. It also gives definitions and translations for rather obscure political grounds.