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.
Gammy is probably a version of game, meaning lame. Cassidy claims that it comes from the Irish cam meaning crooked. He is probably right but this claim did not originate with him. My copy of Collins English Dictionary (published in 1990) gives this as coming from Irish cam as well.