alliance

n.

1. The state of being allied

   connection, adherence, membership, affinity, concurrence, participation, cooperation, support, collusion, union, interrelation, concord, agreement, common understanding, marriage, matrimony, betrothal, kinship, relation, collaboration, fraternization, consanguinity, federation, communion, entente, engagement, friendship, partnership, coalition, association, affiliation, alignment, confederation, implication, bond, accord, congruity, mutuality, tie.

   Antonyms separation*, rupture*, repudiation. *

2. The act of joining

   fusion, combination, coupling; see union 1.

3. A union

   league, union, federation, coalition, confederacy, confederation, bloc, bund, association, partnership, community, pact, treaty, entente, compact, cooperative, co-op, consortium, syndicate, corporation, company, combination, merger, conglomerate, cartel, trust, combine, conspiracy, network, ring, party, band, group, consociation; see also organization 3.

alliance refers to any association entered into for mutual benefit; league, often interchangeable with alliance, stresses formality of organization and definiteness of purpose; coalition implies a temporary alliance of opposing parties, factions, etc., as in times of emergency; confederacy and confederation in political usage refer to a combination of independent states for the joint exercise of certain governmental functions, as defense or customs; union implies a close, permanent alliance and suggests complete unity of purpose and interest