accession
noun [ U ] uk/əkˈseʃ.ən/ us/əkˈseʃ.ən/
formal登基;就职
the time when someone starts a position of authority, especially a king or queen
1926 was the year of Emperor Hirohito's accession to the throne. 1926年日本天皇裕仁即位。
Compare: elevation (IMPORTANCE)
正式加入（国际组织）;签署（条约）
the time when a country officially joins a group of countries or signs an agreement
Poland's accession to the EU 波兰加入欧盟这一情况