Everybody knows the Australian expression (fair) dinkum, but where does it come from? Bruce Moore, who is currently editing the second edition of the Australian National Dictionary, has the answer in an Ozwords post (excerpted from his book What’s Their Story? A History of Australian Words); after laying out a couple of folk etymologies (from “fair drinking”; from Cantonese “‘ting kum’ meaning genuine gold”), he gets down to brass tacks:
A major argument against the purported Chinese origin of dinkum is the fact that the word is attested in British dialects, and that even fair dinkum appears in one of those dialects. A large number of Australian words derive from British dialects, and dinkum is one of them. In the dialects of Lincolnshire and Derbyshire there is a word dinkum that means ‘work; a fair share of work’. There is an 1891 record from a coal-miner who says ‘I can stand plenty o’ dincum’, that is, ‘I can put up with any amount of fair work’; and from north Lincolnshire there is the record of a person who says ‘You have gotten to do your dinkum’. The first record of the word in Australia has this meaning. It occurs in Rolf Boldrewood’s Robbery Under Arms (1888): ‘It took us an hour’s hard dinkum to get near the peak’, that is, ‘an hour’s hard work’. A more recent Lincolnshire dictionary defines dinkum: ‘It means to give fair or deserved punishment to; the correct punishment, justice; to do what is fair and right.’ The Essex dialect has dinkum meaning ‘above-board, honest’. More importantly, in the north Lincolnshire dialect there occurs the idiom fair dinkum meaning ‘fair play’, ‘fair dealing’, ‘that which is just and equitable’. In fact, the notion of ‘fairness’ has always been associated with dinkum. It is from this connotation of ‘fairness’ that the particularly Australian meaning ‘reliable, genuine, honest, true’ developed in the first decade of the twentieth century. This dialect evidence is so dinkum that we do not need to look elsewhere, and certainly not to Chinese miners.
He goes on to tell a great WWI spy story and concludes, “Dinkum was one of those words that served to articulate Australian values during the First World War—it belongs, especially, with Anzac, digger, and Aussie, and is the opposite of furphy.”