Where does “aussie” come from?

aussie (English) comes from English Australian, from English Australia, from Latin terra austrālis incōgnita, from Latin auster, from Proto-Italic *austeros.

Ancestry of “aussie”, step by step

Step	Language	Word	Meaning
1	English	Australian	A person from the country of Australia or of...
2	English	Australia	—
3	Latin	terra austrālis incōgnita	—
4	Latin	auster	The south wind; south
5	Proto-Italic	*austeros	—

Every word from Proto-Italic *austeros →

aussie — Etymology, Origin & Word History | Etymology Explorer