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.
You can find an honest and intelligent discussion of the origins of this word here: https://www.etymonline.com/search?q=cantankerous
Cassidy claims that this derives from the ‘Irish’ “Ceanndánacht ársa (pron. k’an danánǝċt’ ársǝ), old obstinacy, aged willfulness, elderly stubbornness.” Leaving aside the badly-done attempt at phonetics with the extra syllable, there is absolutely no evidence of anyone ever using the expression ceanndánacht ársa in the Irish language. It is completely fictional. It is also worth pointing out that there are hundreds of adjectives in English that end in – ous (joyous, kernaptious, captious). The ársa has been randomly stuck on the end of the ceanndánacht in an attempt to explain this problem away.