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, claims that the term moniker for a name or by-name comes from the Irish travellers’ Shelta language, a kind of backslang based on Irish or Gaelic.
This is possible, certainly, and there is no doubt that a version of this word was found in Shelta in the form munik. This may be a disguised version of the Irish word ainm (pronounced annim) but this is not certain. Some have suggested that moniker was borrowed into Shelta from unrelated kinds of slang like the English cant. An article by William Sayers called Moniker: Etymology and Lexicographical History discusses this in depth.
Whether this is true or untrue, the claim that moniker derives from Irish ainm through Shelta was in the public domain decades before Cassidy came along and therefore has no relevance at all to his thesis.