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.
According to Cassidy, the English word sneak comes from the Irish snighim (sním in the modern, post-reform spelling). He also claims that the Barnhart Dictionary of English Etymology gives this Irish origin. I haven’t got a copy of Barnhart’s and I can’t be bothered to go and look for one, but this claim seems unlikely, given that all the other dictionaries trace it, quite logically, to the Old English snican which is related to cognates in the other Germanic languages as well as to the root of the English word snake.
As usual, Cassidy is being economical with the truth here by ignoring what the mainstream dictionaries say. Snighim is also an unsuitable source for a word used of people, anyway, because it is used for slow-moving animals like snails and slugs. It doesn’t mean to move sneakily or furtively. However, in any case, the word sneak has an impeccable Germanic origin and so it can’t come from Irish.