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