1690s, originally in reference to aboriginal inhabitants, from Australia + -an. As an adjective by 1814. Australianism in speech is attested from 1891.
Entries linking to australian
Australia
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).
-an
word-forming element meaning "pertaining to," from Latin -anus, adjective suffix, in some cases via French -ain, -en. From PIE *-no-.