UK remains a great power and has significant economic, cultural, military, scientific, technological and political influence internationally. The United Kingdom has the world's sixth-largest economy by nominal gross domestic product (GDP), and the eighth-largest by purchasing power parity. It has a high-income economy and a very high Human Development Index rating, ranking 18th in the world. It also performs well in international rankings of education, healthcare, and life expectancy. It is a recognised nuclear state and is ranked fourth globally in military expenditure. It has been a permanent member of the United Nations Security Council since its first session in 1946. The United Kingdom is a member of the Commonwealth of Nations, the Council of Europe, the G7, the Group of Ten, the G20, Five Eyes, the United Nations, NATO, AUKUS, the Organisation for Economic Co-operation and Development (OECD), Interpol, and the World Trade Organization (WTO). The UK is also considered a part of the "Big Four", or G4, an unofficial grouping of important European nations. It was a member state of the European Communities (EC) and its successor, the European Union (EU), from its accession in 1973 until its withdrawal in 2020 following a referendum held in 2016. Etymology and terminology In , Britannia referred to the Roman province that encompassed modern day England and Wales. Great Britain encompassed the whole island, taking in the land north of the River Forth known to the Romans as Caledonia in modern Scotland (i.e. "greater" Britain). In the Middle Ages, the name "Britain" was also applied to a small part of France now known as Brittany. As a result, Great Britain (likely from the French "") came into use to refer specifically to the island, with Brittany often referred to as "Little Britain". However, that name had no official significance until 1707, when the island's kingdoms of England and Scotland were united as the Kingdom of Great Britain. The Acts of Union 1707 declared that the Kingdom of England and Kingdom of Scotland were "United into One Kingdom by the Name of Great Britain". The term "United Kingdom" has occasionally been used as a description for the former Kingdom of Great Britain, although its official name from 1707 to 1800 was simply "Great Britain". The Acts of Union 1800 united the kingdoms of Great Britain and Ireland in 1801, forming the United Kingdom of Great Britain and Ireland. Following the partition of