Green’s Dictionary of Slang

dinkum n.

[dial. dinkum, a fair share of work]

1. (Aus.) work, esp. hard work, a due share of work.

[Aus]‘Rolf Boldrewood’ Robbery Under Arms (1922) 30: It took us an hour’s hard dinkum to get near the peak.
[Aus]Baker Popular Dict. Aus. Sl. 23: Dinkum, hard work or honest toil.
[Aus]G.A. Wilkes Exploring Aus. Eng. 14: Miners in Derbyshire, for example, used dinkum to mean ‘work’, especially hard work [...] From meaning ‘strenuous effort’, dinkum came to mean ‘genuine’ or ‘authentic’, and gained a much wider currency in Australia than it had in the English county from which it came.

2. (also dincum) the truth.

[NZ]N.Z. Truth 4 Aug. 4/7: Then I told him the straight dincum.
[Aus]C.E.W. Bean Anzac Book 56/1: I was on the beach one day when a friend met me and asked if I had heard the latest dinkum.
[Aus]Aussie (France) XII Mar. 1/1: They separated it from the ice, thawed it out, and delightedly absorbed the retrieved liquid joy. That’s dinkum.
[Aus]Queenslander (Brisbane) 28 Nov. 6/2: ‘A friend? Is that dinkum?’ ‘Certainly’.
[Aus]Western Mail (Perth) 4 June 2/2: He seems to be a cross between a squarehead and a Jap.
[Aus]N. Pulliam I Travelled a Lonely Land (1957) 232/2: dinkum (dinky, dinkum oil) – true or truth.
[Aus]D. Niland Big Smoke 211: Why didn’t I take all your money? [...] Why did I only take sixpence if it wasn’t dinkum?
[Aus](con. 1941) R. Beilby Gunner 167: Why would I want to have you on? It’s dinkum, I tell you, the good oil.

3. an Australian, spec. an Australian soldier in WWI .

[Aus]Aussie (France) 18 Jan. 3/1: ‘And how often do you get to leave Australia?’ asked the inquisitive old lady. / ‘Once every war,’ replied one of the dinkums; ‘at the end of it.’.
[Aus]Kia Ora Coo-ee 15 Apr. 2/2: Cooking for a mob of Dinkums is about the most thankless job that I know of, and in my time I have tackled all kinds of employment.

4. something genuine.

[US]P. Corris ‘Stockyards at Jerilderie’ in Heroin Annie [e-book] That made three Castletons, two fakes and a dinkum.