1766 in geography, from French Australasie (De Brosses, 1756), "Australia and neighboring islands," also used later in zoology in a somewhat different sense (with reference to Wallace's line); see Australia + Asia. Related: Australasian.
from Latin Terra Australis (16c.), from australis "southern" + -ia. A hypothetical southern continent, known as terra australis incognita, had been proposed since 2c. Dutch explorers called the newfound continent New Holland; the current name was suggested 1814 by Matthew Flinders as an improvement over Terra Australis "as being more agreeable to the ear, and an assimilation to the name of the other great portions of the earth" ["Voyage to Terra Australis"]. In 1817 Gov. Lachlan Macquarie, having read Flinders' suggestion, began using it in official correspondence. The ultimate source is Latin auster "south wind," hence, "the south country" (see austral).
c. 1300, from Latin Asia, from Greek Asia, speculated to be from Akkadian asu "to go out, to rise," in reference to the sun, thus "the land of the sunrise." Used by the early Greeks of what later was known as Asia Minor; by Pliny of the whole continent.
<a href="https://www.etymonline.com/word/Australasia">Etymology of Australasia by etymonline</a>
Harper, D. (n.d.). Etymology of Australasia. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/Australasia