Green’s Dictionary of Slang

(Aus., also dinckum) honest, genuine; esp. as fair dinkum adj.; thus dinkumest.

1894		Star (Canterbury, NZ) 12 Dec. 3/2: Australian slang is the weirdest in the world. ‘Fair dinkum’ in that lingo means a real Australian.
1905		Duke Tritton’s Letter n.p.: I saw a lot of Joe Blakes, but I don’t know if they were dinkum or just the after effects of the grog.
1913		Sport (Adelaide) 15 Mar. 12/2: They Say [...] That Dave O will find himself in a breach of promise case if he isn't dinkum to that tart of his .
1914		Sport (Adelaide) 8 May 4/5: Who was the little girl [...] Is she the dinckum one?
1917		Truth (Wellington) 13 Oct 5/7: Mine host of the Albert is known as a ‘sport’ [...] He’s a dinkum good fellow, and a bosker good friend.
1918		Aussie (France) 8 Oct. 14/2: He was the dinkumest looking devil-dodger ever I’ve seen.
1924		C.J. Dennis ‘A Woman’s Way’ in Chisholm (1951) 89: Me yap’s a dud / [...] / My conversation ain’t the dinkum brand.
1924		L. O’Neil Dinkum Aussie and Other Poems 3: It’s a dinkum Australia for me!
1924		E.G. Murphy ‘Dossin’ Outer Doors’ in Dryblower’s Verses 5: I ain’t a scientific bloke, but spare me dinkum days, / If I tumble to this josser and his noo fandangled ways.
1930		K.S. Prichard Haxby’s Circus 131: Come on, if you’re a dinkum fortune-teller you ought to be able to do that?
1933		Era (London) 1 Feb. 9/3: Ben Travers has struck the dinkum topical oil.
1941		K. Tennant Battlers 96: I tell you them chaps are dinkum shearers.
1953		I. Hamilton Till Human Voices Wake Us 129: Cedric was a dinkum neurotic.
1960		A. Seymour One Day of the Year (1977) II iii: I think she was dinkum.
1960		‘Nino Culotta’ Cop This Lot 5: Joe says spirit is the wrong word, because ‘dinkum Aussies’ only drink beer.
1977		in K. Gilbert Living Black 87: I was still not happy about the way they were implementing policy and realized that they were not really dinkum about Aboriginal self-determination.
1982		J. Davis Dreamers 86: Git up an’ show ’im a real middar. Go on, oldy, a real dinkum yahllarah.
1988		McGill Dict. of Kiwi Sl. 36/2: dinkum genuine or fair, often expressed as fair dinkum, dinky-di and dinkum oil (the truth), and as dinkum Kiwi; popularised in Australasia from Lincolnshire dialect word ‘dinkum’, an equitable share of work, and ‘fair dinkum’, fair play, with Gloucestershire and Derbyshire dialects also regarding dinkum as working hard.
2001		OnLine Dict. of Playground Sl. 🌐 dinkum n. good, reliable honest. When used with ‘Fair’, it can be a query regarding authenticity, e.g. ‘Is that fair dinkum?’.
2005		C. Hindrum in Tasmanian Times 4 Feb. 🌐 How fair bloody blowfly dinkum Aussie is tryin’ to get a fair go?