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 is an American slang term meaning completely. There is no reason to suppose that it isn’t composed of the English words for and fair, on the pattern of for good meaning ‘forever’. There are many Americanisms that use for, such as for real and for sure.
Cassidy’s claim is that this comes from the Irish foirfe, which means ‘perfect’ and is pronounced forrifa. Why should this be any more likely than for + fair in English?