n. 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.n. Voluntary union of individual persons, parties, or states; particularly, a temporary combining of parties or factions for the attainment of a special end; alliance.n. Synonyms Alliance, League, Confederacy, etc. (see alliance), combination, copartnership.