Australian English is a major variety of the English language, spoken everywhere in Australia.
Although it has no official status in the Constitution, Aussie English is the country's de facto official language and is the first language of the majority of the population.

 It differs from other varieties of English in vocabulary, accent, pronunciation, register, grammar and spelling and has developed along a different track to British or US English, with some vocabulary of its own. There are particular words and phrases that are uniquely Australian, meaningless to many from outside the country, but part of what binds Aussies to each other.

The history of Aussie English reflects the history of the country as a whole — Aboriginal words, convict slang and words from various migrant groups have all been assimilated.

Indigenous Aboriginal Languages

Long before a word of English was ever spoken in Australia, the Aboriginal languages were heard all over the continent. Each Aboriginal grouping has its own language, but those languages spoken close to what later became the main centres of European population were those which have had the most influence on modern Aussie English.

Commonly used Aboriginal words include many animal names, such as kookaburra, koala, wallaby and dingo.

Many Australian place names are Aboriginal — the capital Canberra is so‑named because it means ‘meeting place’.

Other Aboriginal words common in Aussie English include yakka, meaning work–normally used as part of the phrase hard yakka, and cooee, first used by Aboriginal people calling each other through the bush.

Aboriginal words are likely to have been absorbed into Aussie English as local leaders from both native groups and colonists tried to find some tentative common ground; and as the new arrivals sought to find names for the strange new things they were seeing.

Immigrant Influences & New Australians

Whether convicts or willing migrants, the Europeans who found their way to Australia from the eighteenth century onwards came from a wide range of different groups.

At that time, there were great differences between different British English dialects, so that convicts from different regions of England, Scotland, Wales and Ireland would all have spoken very differently. Some would not have spoken English at all – being Irish or Scots Gaelic or Welsh speakers.

To understand each other, these groups would have begun to create a common language, and words from various dialects would have become part of a new slang and new idioms.

It was almost as if an informal Australian school of English and Irish arrivals alike had set itself up. Words which found their way into the language via the convicts include tucker, an Irish word for food, and swag a word from the criminal underworld meaning a parcel of goods taken by a thief, but coming to mean a bushman's bag.

The children of those early settlers would have been keen to mark themselves out as Australians, rather than Irish or English, and that meant that new accents and speech patterns developed as quickly as the colony itself did.

The Gold Rush & The First World War

This era brought words such as fossick and digger into common usage.
Many terms come from the bushranger tradition, such as bush telegraph.

WWⅠ then added another layer of slang, such as dinkum , meaning genuine or real. Australian English is peppered with unique slang words and particular types of phraseology.

Diminutives in Aussie English

The use of diminutive forms of words such as arvo for afternoon or barbie for barbecue is common.

While many languages make use of diminutives, Aussie English uses them extensively – there are over 5,000 identified diminutives in use in Australia.

There is no better way of life in the world than that of the Australian.
I firmly believe this. The grumbling, growling, cursing, profane, laughing, beer drinking, abusive, loyal-to-his-mates Australian is one of the few free men left on this earth.
He fears no one, crawls to no one, bludgers on no one, and acknowledges no master.
Learn his way. Learn his language. Get yourself accepted as one of him; and you will enter a world that you never dreamed existed.
And once you have entered it, you will never leave it.
Nino Cullotta : They're a Weird Mob (1957)