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.
Big shot is first found in American slang in the 1920s. It is thought to be associated with the Prohibition-era gangsters who fought their way to the top by shooting people. This is the entirely reasonable claim made by most etymologists.
Cassidy’s claim is that this comes from the Scottish Gaelic word for gem or jewel, seòd, which is sometimes used in poetry as a figurative term for a valiant person. It is not used this way in Irish, or outside of poetry. The idea that this is the source of the English slang ‘big shot’ is highly improbable and not supported by any evidence.