accession

1 a : increase by something added b : acquisition of additional property (as by growth or increase of existing property)
2 : something added : acquisition
3 : the act of assenting or agreeing
4 a : the act of becoming joined : adherence b : the act by which one nation becomes party to an agreement already in force between other powers
5 a : an act of coming near or to : approach, admittance b : the act of coming to high office or a position of honor or power <her accession to power>
6 : a sudden fit or outburst : access

— ac·ces·sion·al \-ˈsesh-nÉ™l, -ˈse-shÉ™-n^É™l\ adjective