As I have stated over and over again here, Cassidy made no valid contribution to scholarship. His idea of research was to find a word or phrase in English, ignore any origins which had been suggested (or even proven) by mainstream scholarship, and construct his own ‘source’ by combining random bits of Irish he found in a dictionary and didn’t even know how to pronounce. To cover his worthless arse, he constructed a tissue of lies about a conspiracy by Anglophile linguists who were trying to cover up the extent of Irish influence on English, a tissue of lies which has resulted in any individual who criticises Cassidy on linguistic grounds being immediately attacked by trolls for being anti-Irish and a stooge of some fictional cabal of ‘dictionary dudes’. The fact is, of course, that Cassidy’s supporters are the unwitting stooges of a con-man who was completely ignorant of every aspect of Irish culture.
There are probably about seventy or eighty words in the English dictionaries which derive from Irish, perhaps a few more. A re-evaluation of the Irish influence on English might produce a handful of other candidates but it would only be a handful. The undeniable fact is that Irish had relatively little influence on the vocabulary of English.
Does this mean that Irish had no influence at all on English? Not necessarily.
There are a handful of phrases in English, typically Americanisms, which have clear parallels in Irish. One of them is ‘kiss my arse’. Everyone knows the phrase póg mo thóin in Irish. Of course, as an expression of contempt, it is easily understood, and it may have been found in other languages, such as Yiddish or Italian, but if someone can establish that there is no evidence for its existence in English or any other candidate language apart from Irish before the recent period, that’s a good indication that this is a phrase derived from Irish.
Another one which stands out is the phrase ‘to hit the road’. An bóthar a bhualadh (to hit the road) is a common idiom in Irish.
Yet another common one is ‘I wouldn’t put it past him.’ This is a literal translation of the Irish phrase Ní chuirfinn thairis é. If scholars can prove that this is an Americanism which wasn’t in English English a few hundred years ago, then the Irish origin becomes likely.
There is another one which I have often wondered about, the phrase ‘a trout in the milk’. This is not a common phrase, but it was used by Henry Thoreau – ‘Some circumstantial evidence is very strong, like when you find a trout in the milk.’ In Irish, an breac sa bhainne (the trout in the milk) is a common phrase meaning the fly in the ointment, the thing that spoils something. Thoreau used it differently and it is believed to be a reference to the watering of milk by dairymen, so it could be a pure coincidence, but it could also be that he had heard the phrase somewhere and liked the sound of it.
I suspect that an analysis of idioms and expressions found in the speech of American urban communities would show quite a few of these calques (a word-for-word translation from one language to another) as they are known in linguistic circles. It would be interesting to see a proper study of the influence of Irish on American speech, done by a genuine scholar and not by an incompetent flake like Cassidy.