The Australian-English noun dunny denotes a toilet, especially an outside toilet.

It is a shortened form of the British-English noun dunnekin, denoting an outside toilet.

The noun dunnekin is probably from:
– a word denoting excrement (perhaps ultimately a variant of dung);
– the noun ken, denoting a house.

The noun dunny has been used in various Australian-English phrases expressing notions such as conspicuousness, loneliness, ill luck, etc.:

■ Conspicuousness (in the phrase like a dunny in a desert)—two examples:

1-: From The Ridge and the River (Sydney: Angus and Robertson, 1952), by Thomas Arthur Guy Hungerford (1915-2011):

Right now there might be a Shinto under every bush, and me stuck out like a dunny in a desert.

2-: From The Riders, by Tim Winton (born 1960)—as published in The Canberra Times (Canberra, Australian Capital Territory) of Sunday 28^th August 1994:

Long ago he’d confronted the fact that he looked like an axe-murderer, a sniffer of bicycle seats. He stuck out like a dunny in a desert. He frightened the French and caused the English to perspire. Among Greeks he was no great shakes, but he’d yet to find out about the Irish. What a face.

■ Loneliness (in the phrase like a country dunny)—three examples:

1-: From Australia Speaks: A Supplement to “The Australian Language” (Sydney: Shakespeare Head Press, 1953), by Sidney John Baker (1912-1976):

Loneliness All by himself like a country dunny.

2-: From The Sword and the Blossom (London: The Hogarth Press Ltd, 1968), by Ray Parkin (1910-2005):

The Dutch had packed it in and left us on our own like a country dunny.
[…]
Dunny: A privy. Like a country dunny: Isolated, all alone.

3-: From the review of The Dinkum Dictionary: A Ripper Guide to Aussie English (Ringwood (Victoria): Viking O’Neil, 1988), by Lenie (Midge) Johansen—review by Ralph Elliott, published in The Canberra Times (Canberra, Australian Capital Territory) of Saturday 3^rd September 1988:

Two distinctive features of this Oz word-hoard merit special mention. One is the classified list of words at the end, some 30 pages long, devoted to such major Australian concerns as drink, sex, trickery, stupidity, and the calls of nature. They will teach you a great deal about the national character we hear so much about these days when, all alone like a country dunny, you have the leisure and concentration to perfect your knowledge of our language.

■ Ill luck (in phrases of the form if it was raining —)—for example:

From Sowers of the Wind: A Novel of the Occupation of Japan (Sydney: Angus and Robertson, 1954), by Thomas Arthur Guy Hungerford (1915-2011):

“Damn all!” the man called Nocker grunted. “If it was rainin’ palaces I’d get hit on the head with the handle of the dunny door.”

■ An exceptional sexual partner (in the phrase to bang like a dunny door)—for example:

From Bazza brings it up, the account of the official Australian world premiere of The Adventures of Barry McKenzie ¹—account by Sandra Hall, published in The Bulletin (Sydney, New South Wales) of Saturday 21^st October 1972:

Barry Crocker plays him [i.e., Barry McKenzie] as a walking accident. The deadpan feeling of the comic strip has become all vulnerable, big-eyed and ingenuous. “If it was raining sheilas,” he says in the producer, Phillip Adams’ favorite line, “I’d be washed down the drain with a poofter.” And it’s because he never will realise his ambition to find a jam tart who bangs like a dunny door that the well-prepared (or warned) opening night audience loved him.

¹ The Adventures of Barry McKenzie (1972) is an Australian comedy film by the Australian film director Bruce Beresford (born 1940), starring the Australian comedian Barry Crocker (born 1935), telling the story of an Australian yobbo on his travels to the United Kingdom. Barry ‘Bazza’ McKenzie was originally a character created by the Australian comedian Barry Humphries (born 1934) for a cartoon strip in the British satirical magazine Private Eye. (Barry Humphries also created and interpreted Dame Edna Everage, a fictional character satirising the average Australian housewife.)

■ Malediction (in the phrase may your chooks turn into emus and kick your dunny down)—two examples:

1-: From Brushing up ‘Bazza’ for UK audiences, a correspondence from London published in The Sydney Morning Herald (Sydney, New South Wales) of Wednesday 21^st February 1973—the following is about the release in the United Kingdom of the above-mentioned 1972 comedy film, The Adventures of Barry McKenzie:

Humphries gave some examples of how sub-titles will be used in the “English” version of the film.
Where Barry McKenzie says to an upper-class Englishman in one scene: “I hope your chooks turn into emus and kick down your dunny,” a translation line will appear on the screen saying: “Destroy your outdoor toilet.”

2-: From a letter published in Tharunka (Kensington, New South Wales) of Wednesday 21^st May 1975—Tharunka is a student magazine published at the University of New South Wales:

Dear Editors,
I realise that this letter will probably not be read and will definitely not be printed in your FREE press, but I feel that it is my duty to get off my chest what has been giving me the grizzlies for weeks.
[…]
Right—go ahead and tear up this letter, at least you know I said it, and I mean it! To you goddamn editors: “May the Bird of Paradise fly up your nostrils”. “May your chickens grow up into emus and kick your dunny door down” and “May the dead horse you’ve been flogging all these years jump up and fuck hell out of you.”!
Yours maliciously
Melba (an art fart)

■ Togetherness—for example:

From the review of an album by the Australian group Captain Matchbox Whoopee Band—review by Tony Catterall, published in The Canberra Times (Canberra, Australian Capital Territory) of Monday 8^th December 1975:

Take the melodramatic, mock-heroic love pledge ‘Forever’, which as well as containing the immortal words “And like flies on the dunny door, we will stick together” ends with a loud, clear belch.
That might be going a bit far into deliberate bad taste, but then whatever provokes a reaction can be said to have done its job.

■ Australianness (in the phrase as Australian as a slab off a dunny door)—for example:

From Aussie Comics: From Mo to Hogan, by Ian Moffitt, published in The Bulletin (Sydney, New South Wales) of Saturday 1^st May 1976—the following is about “thousands of Australians who needed a more acute lunacy”:

Monty Python’s Flying Circus has supplied that need for a later generation; the minority need for electric, insane communication—a mental break-out from a stifling, conservative society. Hogan ² does not fill it for these people: like a dunny door, he’s a genuine slab of Australia, but he is also, often, just as wooden.

² This refers to the Australian actor Paul Hogan (born 1939).

■ Uselessness (in the phrase as useful as a glass door on a dunny)—for example:

From Dark Clouds on the Mountain (Melbourne: Hybrid Publishers, 2010), by the historian and novelist John Tully (born 1947):

I said that I couldn’t see any of the blokes getting involved in anything that vicious but there was one fella who could have been in it. ‘Asset’, we called him, on account of him being about as useful as a glass door on a dunny. Look, it’s pretty hard to get the sack round here. The union won’t stand for bullshit and all up, it’s a fairly democratic place to work compared with some of the places I’ve been. But this bloke—Wally Boyce was his name—well, he was truly bloody hopeless and it go to the point where they sacked him.