I had meant to write about this word ages ago but somehow was distracted and never got around to writing the post. The word gazoony was apparently originally a fairground or carny term for a young, inexperienced worker. A search on Google shows that in some circles it now means a young man in a gay relationship with an older man.
Cassidy claims that this derives from an Irish word, garsún, meaning a boy.
There is nothing inherently improbable about this. The word garsún does exist and it does mean boy. Any Cassidy supporter reading this will probably be tutting already. So there’s an Irish word which sounds similar and means boy, yet they’re still not happy! How much evidence do these people need?
Sorry, but I need a bit more evidence than this. For one thing, garsún may be an Irish word, but it’s not of Irish origin. Garsún derives, of course, from Norman French. Anyone who learned French at school will recognise the word garçon which means both boy and waiter. Cassidy actually mentions garçon and the Latin word garcio from which it derives, but only with cf., which means compare. He doesn’t state that the Irish word is a loanword.
It entered Irish in two forms, as garsún and as gasúr. The dialects of Connemara and of Ulster use gasúr (though the meaning is different in the two areas – gasúr is a boy in Ulster but a child of either gender in Connemara). In Munster they say garsún. It isn’t used in Irish outside Munster, to the best of my knowledge. In Hiberno-English, the word has also been borrowed as gossoon.
The problem with Cassidy’s claim is this. How can we be sure it didn’t come directly from French? There are plenty of French Canadians and there were plenty of French speakers in places like Maine and Louisiana. Cassidy doesn’t try to exclude the French origin from the equation. A real researcher would need to do this and they would also have to make sure that the word doesn’t have an equivalent in some other Romance language, such as Italian. (The official Italian for a boy is ragazzo, sometimes shortened to gazzo, but there are lots of dialects in Italy and carnival slang is known to contain a large Italian element through the jargon known as Polari.)
In other words, it’s possible that gazoonie comes from garsún or indeed from Hiberno-English gossoon. But it’s also highly likely that it might have come from French and it might well come from some related language. Cassidy decided that because of its appearance, it must come from Irish. But he failed to follow it up with any proper research and that’s why the lexicographers are entirely right to ignore Cassidy’s claim. He didn’t play by the rules and the rules are there to guarantee that books contain the truth (not to arbitrarily exclude Irish or any other language.)