Another ridiculous claim in Daniel Cassidy’s dreckfest How The Irish Invented Slang is that snoot (as in snooty, stuck up) comes from the Irish snua ard. As usual, of course, this is a made up phrase and is not recorded in Irish. Snua is defined as complexion or colour or appearance. Ard means high. So this means ‘a high complexion’ (though there is no evidence in my experience of the language or in the dictionaries that ard would be used in contexts like this the way high is in English, to mean ruddy.) In other words, ‘a high complexion’ is pretty meaningless in Irish and certainly doesn’t convey the idea of snobbishness.
Neither does ‘snooa ard’ sound much like snoot. And then again, there is the fact that snoot is a Scottish variant of snout, meaning nose, and the idea of snobbishness comes from the notion of someone looking down their nose at you. As usual, Cassidy’s claim is just fatuous made-up garbage.