Australian vs Abo

Australian and Abo both are nouns.

Word	Noun	Adjective	Verb	Adverb
Australian	Yes	Yes	No	No
Abo	Yes	No	No	No

As nouns, Abo is a hyponym of Australian; that is, Abo is a word with a more specific, narrower meaning than Australian:

Australian: a native or inhabitant of Australia
Abo: a dark-skinned member of a race of people living in Australia when Europeans arrived

Other hyponyms of Australian include Aborigine, Australian Aborigine, native Australian.

Australian (noun)	Abo (noun)
the Austronesian languages spoken by Australian aborigines	a dark-skinned member of a race of people living in Australia when Europeans arrived
a native or inhabitant of Australia

Australian (adjective)	Abo (adjective)
of or relating to or characteristic of Australia or its inhabitants or its languages