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.
The late Daniel Cassidy, in his etymological hoax, How The Irish Invented Slang, denied that the word squeal, as in “he squealed to the cops”, has anything to do with the noise that a panicking animal makes. He derived it from scaoil, an Irish verb which means release, and can mean to divulge a secret, as in the phrase scaoil sé a rún. However, it is worth noting that squeal is often used as an intransitive verb – you can say “he squealed” and not “he squealed something”. With scaoileadh, you couldn’t do this. It requires an object. The fact is that when people borrow words, they generally use them in the foreign sentence in just the same way as they would be used in the original language.
The word squealer, according to Cassidy, derives from the Irish scaoilteoir, which he says means: ‘a releaser, a divulger; fig. an informer’. The informer part of this definition is fantasy. Scaoilteoir is defined by Ó Dónaill as ‘releaser, discharger, deliverer’. Dinneen defines it as ‘one who sets free, a deliverer’.
Squeal is self-explanatory in English, and there is no need to regard it as loan from Irish or any other language.