coalition

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

• noun An alliance, especially a temporary one, of people, factions, parties, or nations.
• noun A combination into one body; a union.
• noun A long-term cooperative alliance among a small number of male lions or cheetahs, especially to gain access to females or territory.
• noun A transitory association of animals of the same species in which members join forces against another animal or animals to defend against an attack or gain access to a resource.

from The Century Dictionary.

• noun Union in a body or mass; a coming together, as of separate bodies or parts, and their union through natural causes in one mass or whole: as, a coalition of atoms or particles.
• noun Voluntary union of individual persons, parties, or states; particularly, a temporary combining of parties or factions for the attainment of a special end; alliance.
• noun Synonyms Alliance, League, Confederacy, etc. (see alliance), combination, copartnership.

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

• noun The act of coalescing; union into a body or mass, as of separate bodies or parts.
• noun A combination, for temporary purposes, of persons, parties, or states, having different interests.

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

• noun A temporary group or union of organizations, usually formed for a particular advantage.

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

• noun the state of being combined into one body
• noun an organization of people (or countries) involved in a pact or treaty
• noun the union of diverse things into one body or form or group; the growing together of parts