For some time now, some of my on-line friends have advised me to provide a version of CassidySlangScam without the invective aimed at Cassidy and his supporters. In response to that advice, I am working on providing a glossary of the terms in Cassidy’s ludicrous book How The Irish Invented Slang with a short, simple and business-like explanation of why Cassidy’s version is wrong.
As Daniel Cassidy states in his book How The Irish Invented Slang, the word cross is believed to come from Latin crux via Old Irish cros and Old Norse. It gradually supplanted the original word for cross in English, which was rood, as in a rood-screen. The English dictionaries accept that this is the origin of the word and this claim certainly did not originate with Cassidy.
Cant was the criminal argot, the language of the beggars and thieves in Merry England, though sometimes it was also used to mean hypocritical or wheedling speech of any kind. The term is first used in English at the end of the fifteenth or beginning of the sixteenth century.
Most dictionaries say that the word comes from the Latin cantare, to sing, though some trace it to a pair of puritanical preaching brothers called Cant. It has also been suggested (many times) that cant comes from the Irish or Scots Gaelic cain(n)t, meaning speech. This suggestion is not new and was not invented by Cassidy. For example, it is given already in R. McCutcheon’s Modern Language Notes in 1921.
Personally, I find the Irish/Gaelic explanation unlikely because it is found in England at such an early time. There is little evidence for linguistic crossover between the two languages as early as this, though there are occasional – and well-attested – words which did enter English at an early period. For example, brat is a Celtic word for a cloak which was already found in Old English (this means a rag in English dialect and may be the origin of brat as in badly-behaved child, though there is another candidate), while the word cros, an Irish version of Latin crux, was brought to the York area by Vikings who had settled in Ireland and gradually displaced the English term rood, so that cross is the standard term for a cross in English today. However, the few real examples are quite conspicuous and it is very unlikely that cant is a word of Irish origin.