Accession (Noun)
Definition: This refers to when a country officially and formally agrees to an international treaty. It is used specifically when a country becomes a Member State of the European Union. The Member states accede to the Treaty of Rome and other EU treaties by signing accession agreements.
Example: The number of Member States of the EU grew to 28 with the accession of Croatia in 2013.
This word features in Episode 34 of the Study Legal English Podcast.