Accession means formally taking on an important position or role, especially when someone becomes a monarch or leader. When a prince becomes king after his father dies, that moment is called his accession to the throne. Queen Elizabeth II's accession happened in 1952, marking the beginning of her reign.

The word captures something significant about these transitions: they're official, ceremonial moments when power and responsibility formally transfer from one person to another. A company's board might celebrate the accession of a new CEO, or historians might study what happened during a president's accession to office.

Accession can also mean acquiring something new, particularly in museums or libraries. When a museum gains a new painting for its collection, that painting becomes an accession. Libraries track their accessions, keeping careful records of every new book they acquire. In this sense, the word means both the act of receiving something and the thing received.