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.
Daniel Cassidy, in his etymological hoax, How The Irish Invented Slang, claimed that slug (meaning a swallow or a mouthful) comes from the Irish word slog or slogadh, which means to swallow. On the face of it, this seems sensible enough and not surprisingly, this is a very old claim. For example, a document on Irish words in the English of Kildare published in 1914 gives it as:
Slog (slug), a sup.
This derivation could be true but the real situation is rather more complicated. Reality is frequently more complex and less neat than the constructs of pseudo-scholars like Daniel Cassidy.
The complicating factor is the existence of the term slug for a bullet, which dates back to the 17th century and is presumably derived from the animal because of some imagined similarity between bullets and slugs. This then gave rise to an (attested) expression ‘to fire a slug’, which meant to take a drink. This is similar to the common use of the term shot for a drink of whiskey or other spirits.
The Irish origin from slog is not impossible but as we have said, this did not originate with Daniel Cassidy.