The name Britain comes from the Brittonic word Prydain, which was first used by the Romans to refer to the island. The name is thought to be derived from a Celtic root word meaning "painted" or "decorated", possibly referring to the body art of the ancient Britons.
The term Great Britain was first used in the 16th century to distinguish the island from the smaller island of Brittany, which is located in northwestern France. The name became more widely used in the 18th and 19th centuries, as the United Kingdom became a major power in the world.
Today, the term Great Britain is still used to refer to the island, although the term Britain is more commonly used.