Definition of Tonga from the Oxford Advanced Learner's Dictionary

a country in the south-west Pacific, consisting of over 150 small islands, many of them without inhabitants. Its former name was the Friendly Islands. It was part of the British Empire from 1900 until 1970, when it became independent and a member of the Commonwealth. It is ruled by a king or queen. Its capital city is Nuku'alofa and its official language is English. See related entries: Countries and continents
See the Oxford Advanced American Dictionary entry: Tonga