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.
Cassidy claims that the word darb means any excellent person or remarkable thing. He claims that it derives from Shelta, a kind of Irish-based backslang used by the Irish Travellers. He cites the word daarp, which he claims is a Shelta adjective meaning true, genuine, real. In reality, the word d’arp is given in The Secret Languages of Ireland as a word for true or genuine. This would be pronounced jarp and is derived from the Irish dearbh, meaning true or genuine.
Collins Dictionary takes the view that the American slang term darb is a contraction of the earlier slang term darby, meaning ready money, originally, a strict usurer’s bond, short for Father Darby’s bond. If it comes from darby, then plainly it doesn’t come from d’arp.