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.
This seems to be a common expression in America but it is completely unknown in Ireland. It is used to mean ‘bottom’ and seems to be an informal and inoffensive word often used with children. According to Daniel Cassidy in his work of pseudo-etymology, How The Irish Invented Slang, this word derives from the Irish word ciste meaning ‘chest, coffer, treasure, fund’. This is nonsense. The Irish word is derived from Latin, either directly or via an Old English borrowing.
The original Latin word is cista, which means a chest or box. This Latin word was also borrowed into German as Kiste, which is pronounced quite like keister. The German expression Kiste has several meanings. One is trunk or case and the other is what you use to sit on a trunk or case, your backside. This is the origin of the word keister in American speech. As I have already said, the term keister is completely unknown in Irish English, and the word ciste does not have the meaning of backside, so Cassidy’s claim is obviously incorrect.