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.
Gigger is a cant (criminal slang) expression for a door. According to the late Daniel Cassidy, this word comes from the Irish gíogaire, meaning a squeaker.
There is one glaring problem with this claim. The English g can be hard as in goblet or soft as in ginger. The evidence suggests that gigger is as often written as jigger than as gigger. If its primary pronunciation is jigger, it definitely doesn’t come from Irish gíog. You can find some more information here:
It is clearly related to terms like jigsaw, in that jig refers to the moving portions of a device or machine.