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.
Daniel Cassidy, in his book How The Irish Invented Slang, claimed that the word jazz (and its earlier form jass) derive from the Irish word teas, meaning heat. This is highly unlikely. There are dozens of theories about the origins of the word jazz, which first occurred in a musical context in 1912. Here’s a brief selection of them:
From the word jasmine, because jasmine oil was used in brothels and became associated with sex.
From Creole brothels where jezebels (prostitutes) worked.
From Creole patois jass “strenuous activity,” especially “sexual intercourse.”
From a black entertainer called Jas (James).
From a black entertainer called Chas (Charles).
From a Chicago musician called Jasbo (Jasper) Brown.
From jaser, a French word meaning conversation or intercourse, in various senses.
From the French word chasser, to hunt.
From a variant of jasm, a slang term dating back to 1860 that means ‘pep, energy’ and is related to jism for semen. Cassidy claimed that this derives from Irish too, but this is incorrect.
From various African languages, words like Mandingo jasi, ‘to become unlike oneself’.
From deas, the Irish for nice.
Cassidy’s claim that the word comes from teas is no more likely than any other claim on the list, and considerably less likely than most. It should also be noted that Cassidy demonstrated his total ignorance of phonetics and phonology in relation to the words jazz, jass, jazzbo, jazzy and jasm. His versions of the pronunciation of these words, such as j’ass, chass, j’asbah, ch’asbah, t’aspǝ, are completely fake. They have nothing to do with genuine linguistics. To give just one example, j is generally used in linguistics to express the sound usually written in English as a y. Also, Cassidy believed that a slender t in Ulster Irish is pronounced with the j sound of English jam. This is untrue.
Cassidy’s definition of the word teas is also fake. It does not mean “heat, excitement or passion”. You can find an accurate definition here: https://www.teanglann.ie/en/fgb/teas