accession

noun

1.
a process of increasing by addition (as to a collection or group)
2.
(civil law) the right to all of that which your property produces whether by growth or improvement
3.
something added to what you already have
4.
agreeing with or consenting to (often unwillingly)
Derived from:
accede
6.
the act of attaining or gaining access to a new office or right or position (especially the throne)
Derived from:
accede access