"Accession" refers to the act of obtaining or acquiring something, such as new rights, responsibilities, or ownership of something, typically through a formal agreement or process. Full definition
In the present case, a member of the Norvegian Hells Angels was denied entry into Iceland because the Icelandic authorities argued that he played a central role in the final stage of accession of an Icelandic motorcycle club as a new charter in Hells Angels. (europeanlawblog.eu)
Indianapolis Museum of Art Accession Number: 1997.183, Indianapolis Museum of Art Object Type: Visual Works: Paintings (artsy.net)