Definition of "Accession" :

noun: the act of attaining or gaining access to a new office or right or position (especially the throne)

"Elizabeth's accession in 1558."

noun: the right to enter

noun: agreeing with or consenting to (often unwillingly)

"Accession to such demands would set a dangerous precedent."

noun: something added to what you already have

"The librarian shelved the new accessions."

noun: (civil law) the right to all of that which your property produces whether by growth or improvement

noun: a process of increasing by addition (as to a collection or group)

"The art collection grew through accession."

verb: make a record of additions to a collection, such as a library