federation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act of federating, especially a joining together of states into a league or federal union.
• noun A league or association formed by federating, especially a government or political body established through federal union.

from The Century Dictionary.

• noun The act of uniting in confederation by league and covenant.
• noun A league; a confederacy; a federal alliance.
• noun A federal government, as that of the United States, Switzerland, or Germany.
• noun Synonyms See confederation.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of uniting in a league; confederation.
• noun A league; a confederacy; a federal or confederated government.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Act of joining together into a single political entity.
• noun Array of nations or states that are unified under one central authority which is elected by its members.
• noun Any society or organisation formed from separate groups or bodies.
• adjective Australia Of an architectural style popular around the time of federation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a union of political organizations
• noun an organization formed by merging several groups or parties
• noun the act of constituting a political unity out of a number of separate states or colonies or provinces so that each member retains the management of its internal affairs