accession

Concise Oxford English Dictionary © 2008 Oxford University Press:
accession/akˈseʃn/

▶noun

• 1 the attainment of a position of rank.

• 2 the formal acceptance of a treaty or joining of an association.

• 3 a new item added to a collection of books or artefacts.

▶verb record the addition of (a new item) to a library or museum.