noun A nation occupying the whole of the Australian continent, Aboriginal tribes are thought to have migrated from southeastern Asia 20,000 years ago. It's the world's smallest continent, southeast of Asia between the Pacific and Indian oceans. Australia is a commonwealth comprising the continent of Australia, the island state of Tasmania, two external territories, and several dependencies. The first British settlement, a penal colony at Fort Jackson (now part of Sydney), was established in 1788. The present-day states grew as separate colonies; six of them formed a federation in 1901. In 1911 Northern Territory joined the commonwealth and the Capital Territory, site of Canberra, was created. Canberra is the capital and Sydney is the largest city. (Population=18,322,231) It's about 3/4 the size of the continental United States.