accession (Noun) — A process of increasing by addition (as to a collection or group). ex. "the art collection grew through accession"
accession (Noun) — (civil law) the right to all of that which your property produces whether by growth or improvement.
accession (Noun) — Something added to what you already have. ex. "the librarian shelved the new accessions"
accession (Noun) — Agreeing with or consenting to (often unwillingly). ex. "accession to such demands would set a dangerous precedent"
accession (Noun) — The right to enter.
accession (Noun) — The act of attaining or gaining access to a new office or right or position (especially the throne). ex. "Elizabeth's accession in 1558"
accession (Verb) — (recording) make a record of additions to a collection, such as a library.