Charles Mackay (1812 – 1889) is one of the strangest writers and thinkers of the 19th century. He was born in Perth, Scotland, and educated in London. In his youth, he worked as a journalist through French in Belgium. He was a poet and a lexicographer. His fame today rests on the book Extraordinary Popular Delusions and the Madness of Crowds (1841), which is one of the first accounts of pseudoscience and crazy beliefs. Bizarrely, in addition to this book, he also wrote an eccentric work of fake etymology called Gaelic Etymology of the Languages of Western Europe. In this book, his methodology is almost exactly that of Cassidy. He looked at words in other languages and then tried to find a word which could correspond vaguely in sound and meaning. This then became the ‘origin’ of the word, regardless of the evidence of the word’s roots in other languages or any other common sense considerations. The paradox of Mackay’s life is that he was both a great sceptic and a major crank.
Cassidy, of course, was just a major crank. There was no upside to his work. Unsurprisingly, Cassidy quotes Mackay’s ‘etymology’ sometimes as if he were a believable source, as in the case of the word feud, which has nothing to do with the Celtic languages.