one of the Shetland Islands, historic county of Shetland, Scotland, lying in the Atlantic Ocean 16 miles (26 km) southwest of the largest Shetland island, Mainland. Rocky and exposed, Foula has an area of 4 square miles (10 square km). Its cliffs rise to 1,200 feet (400 metres) and are inhabited by numerous seabirds, including the largest colony of great skuas in Great Britain. Foula can be isolated for long periods by bad weather. Common Scandinavian (Viking Norse) was spoken on the island until about 1800.