coalition

n. alliance, union, voluntary joining together, agreement made between two or more parties to work together toward a common goal

A coalition is an among entities, during which they cooperate in joint action, each in their own self-interest. This alliance may be temporary or a matter of convenience. A coalition thus differs from a more formal covenant. Possibly described as a joining of 'factions'.
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Coalition /co·a·li·tion/ the fusion of parts that are normally separate. tarsal coalition the fibrous, cartilaginous, or bony fusion of two or [more]Coalition - Community and Resources

Noun
1. an organization of people (or countries) involved in a pact or treaty
(synonym) alliance, alignment, alinement
(hypernym) organization, organisation
(hyponym) combination
(member-meronym) ally
2. the state of being combined into one body
(synonym) fusion
(hypernym) union, unification
(hyponym) alliance, confederation
(derivation) blend, flux, mix, conflate, commingle, immix, fuse, coalesce, meld, combine, merge
3. the union of diverse things into one body or form or group; the growing together of parts
(synonym) coalescence, coalescency, concretion, conglutination
(hypernym) union, unification, uniting, conjugation, jointure
(derivation) blend, flux, mix, conflate, commingle, immix, fuse, coalesce, meld, combine, merge

n. coalition, league