According to Polynesian Mythology, Tonga was the name of the first woman on the island of "Tonga" and is, hence, the island's name also.
Tonga also means "South" and has come to refer to the entire group of islands which make up the southern portions of central Polynesia. Tradition has it that the Maori tribe sailed from Tonga to New Zealand, following Venus. The Tongan language is, in fact, a very old form of Polynesian.
Finally, Tonga refers to the South-West Wind that blows through the South Pacific. It was the fourth and final wind brought under control by the god Maui.