The name of Australia comes from "terra australis incognita" translation "unknown land of the south"

The name Australia is derived from the Latin Australis, meaning "Southern". Legends of an "unknown land of the south" (terra australis incognita) date back to Roman times and were commonplace in medieval geography but were not based on any documented knowledge of the continent. In 1521 Spaniards were among the first Europeans to sail the Pacific Ocean. The first use of the word Australia in English was in 1625, in "A note of Australia del Espiritu Santo, written by Master Hakluyt", published by Samuel Purchas in Hakluytus Posthumus.

http://en.wikipedia.org/wiki/Australia