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.
It is true that there is a similar word in Irish, as Cassidy claims, the word caidéir. However, caidéir is clearly a borrowing from English, not the other way around. The word cadger is attested in English more than a century before it occurs in Irish for the first time. Cadger may be related to the word codger and to the verb cadge, which have a longer history: https://www.etymonline.com/word/cadge