How to say "union" in Japanese

• 連合れんごうJLPT N2approx.Common
  noun, suru verb, transitive verb, intransitive verbA union or confederation of separate organizations, parties, or states joined into one larger body. This is the word for senses like alliance and combination at the level of groups or nations.
  戦争せんそうは連合軍れんごうぐんの勝利しょうりに終おわった。↗

  The war ended in victory for the Allied Powers.
• 接続せつぞくJLPT N2approx.Common
  noun, suru verb, transitive verb, intransitive verbConnection or attachment: joining one thing to another, such as linking devices or wires. 'Union' is only a marginal sense here; for union as alliance or unity, this is seldom the word you want.
  インターネットの接続せつぞくが遮断しゃだんされた。↗

  My internet connection was cut off.
• 同盟どうめいJLPT N1approx.Common
  noun, suru verb, intransitive verbAn alliance or league: a union of nations, parties, or groups that agree to act together for shared interests. Choose this when 'union' means a pact between parties rather than a merged body.
  戦争せんそうの直前ちょくぜん、日本にっぽんがフランスと同盟どうめいを結むすびました。↗

  Japan entered into an alliance with France just before the war.
• 合体がったいCommon
  noun, suru verb, transitive verb, intransitive verbUnion as physical merging: two or more things combining or coalescing into a single body. Use it for concrete fusion or amalgamation, not for alliances between organizations.
  こういう風ふうに合体がったいすれば、１４ポートのＵＳＢハブになります。↗

  If you combine them in this way, you get a 14 port USB hub.
• 結束けっそくJLPT N1approx.Common
  noun, suru verb, transitive verb, intransitive verbUnion as unity or solidarity: the state of a group whose members are closely bound together. Use it when 'union' means togetherness of people rather than a formal organization.

Use 連合 for a union or confederation of organizations or states, 同盟 for an alliance or league with a shared purpose, 合体 for things physically merging, 結束 for unity or solidarity within a group, while 接続 means connection.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 連合れんごうunion
• 接続せつぞくconnection
• 同盟どうめいalliance
• 合体がったいunion
• 結束けっそくunion
• ユニオンunion
• 接合せつごうunion
• 組合くみあいassociation
• 結合けつごうcombination
• 合同ごうどうcombination
• 合併がっぺいmerger (of companies, towns, etc.)
• 連盟れんめいleague
• 団結だんけつunity
• 連立れんりつcoalition
• 連邦れんぽうfederation (of states)
• 和合わごうharmony
• 和集合わしゅうごうunion
• 合併集合がっぺいしゅうごうunion
• 共用体きょうようたいunion (data type in C and related languages)
• 合一ごういつunification
• 合邦がっぽうmerger (of countries)
• 一致いっちunion
• 合流ごうりゅうjoining (of people, groups, parties, etc.)
• むすびjoin