Tas·ma·ni·a (tāz-mā'nē-ə, -mān'yə) An island state of southeast Australia consisting of the island of Tasmania along with several smaller islands and separated from the mainland by Bass Strait. Abel Tasman explored the island in 1642, naming it Van Diemen's Land. It was renamed in his honor in 1853. Tasmania joined Australia in 1901. Tas·ma'ni·an adj. & n.