Similar word to union:

abutment, accord, agglutination, agreement, amalgam, amalgamation, blend, centralization, coadunation, combination, coming together, commixture, compound, concatenation, conciliation, concord, concurrence, confluence, congregation, conjunction, consolidation, correlation, coupling, fusion, harmony, hookup, incorporation, intercourse, joint, junction, juncture, meeting, melding, merging, mixture, seam, symbiosis, synthesis, tie-in, tie-up, unanimity, unification, unison, uniting, unity