1
- mass noun the attainment or acquisition of a position of rank or power, typically that of monarch or president即位; 就职, 就任：
the Queen's accession to the throne.
女皇即位。
1.1
- the action or process of formally joining or being accepted by an association, institution, or group正式加入, （协会、机构或团体等的）正式接纳：
the accession of Spain and Portugal to the EC.
西班牙和葡萄牙正式加入欧盟。
1.2
- the formal acceptance of a treaty or agreement（对条约或协议的）正式接受：
accession to the Treaty of Rome was effected in 1971.
对罗马条约的接受于1971年生效。
2
- a new item added to an existing collection of books, paintings, or artefacts新藏品（如书籍、绘画或工艺品）。
2.1
- an amount added to an existing quantity of something增加量：
substantial accessions of gold.
黄金库存大增。
with obj.(一般作 be accessioned)
- record the addition of (a new item) to a library, museum, or other collection（图书馆、博物馆等）把（新藏品）登记入册。
词源
late 16th cent. （in the general sense 'something added'）： from Latin accessio（n-）, from the verb accedere 'approach, come to' （see ACCEDE）.