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.
In his etymological hoax, Cassidy claims that the English word muggy comes from the Irish word múchta (smothered), which he claims is pronounced mookta. It can mean muggy (as in aimsir mhúchta) but it is not pronounced mookta. It is pronounced moohta or mookhta, like the ch of loch/lough. Even if it were pronounced with a hard k sound, múchta sounds nothing like muggy.
Back in the real world, muggy comes from a dialect word for fog or humidity, mug, which is of Norse origin.