Another absurd claim in Daniel Cassidy’s idiotic work of fake linguistics, How The Irish Invented Slang, is the one about duke, dukie and dukin’ it out. Cassidy attributes this to the Irish word tuargain (toorgun), which means to pound. This isn’t a perfect match phonetically, though the meaning isn’t too far off. However, we need to look at all the facts before accepting Cassidy’s claim.
Firstly, the basic word here is not dukin’ but duke. Duke has been used as a slang term for the hands since at least the 19th century. The verb ‘dukin’ it out’ is only on record since the 1960s so it’s reasonable to assume that it is a derivative of ‘duke’.
Where does duke come from? The most likely explanation is that it comes from Cockney rhyming slang. Since the mid-18th century, the word ‘fork’ is found as a slang term for hand, for obvious reasons. Then the phrase Duke of York probably gave rise to the term duke for hand.
There is no evidence for tuargain being the origin of these words and it is hard to explain why the word dukes for hands seems to have existed long before the verb dukin’ if the noun is a back-formation from the verb, as Cassidy claims. (A back-formation is a word like burger, which derives from hamburger because people mistakenly believed that the ham referred to the meat.)
As usual, it’s just fanciful bullshit with no evidence to back it up but a slight similarity of sound.