This is yet another ridiculous claim from the pen of the idiot Daniel Cassidy. Again, it relies on borrowing a phrase rather than a word. When people borrow between languages, they tend to borrow individual words. Occasionally they borrow well-known and often-used phrases. They don’t borrow bits of sentences like ‘is right’.
Cassidy claimed that the English slang term square, as in all square or square deal comes from the Irish is cóir, ‘is right’. Why it can’t just come from square as in four-sided and regular and not crooked is never explained but then Cassidy’s ‘research’ is about convincing idiots who’ve already made their minds up by the time they read the blurb on the back cover. It’s not about convincing sensible and intelligent people with inquiring minds.