Merriam-Webster's Collegiate® Dictionary, 11th Edition
ACCESSION
I. noun
Date: 1588
1. increase by something added, acquisition of additional property (as by growth or increase of existing property), something added ; acquisition , the act of assenting or agreeing,
4. the act of becoming joined ; adherence , the act by which one nation becomes party to an agreement already in force between other powers,
5. an act of coming near or to ; approach , admittance , the act of coming to high office or a position of honor or power , a sudden fit or outburst ; access , accessional adjective
II. transitive verb
Date: 1892
to record in order of acquisition