Among Cassidy’s many crazy and unsupported theories was one which has really caught the public’s imagination, the claim that the Dead Rabbits gang, shown in the film Gangs of New York as carrying a dead rabbit on a spike as a totem, really had no connection with rabbits at all and that this name is in truth a phonetic rendering of the Irish ráibéad, meaning a big, hulking person or thing.
First off, there is no doubt that the Dead Rabbits did carry a dead rabbit into battle with them, or at least that this claim was made a long time ago. As far as I’m concerned, that is pretty much that, because once you accept that their name is connected to dead rabbits, any claim that the name is Irish becomes pointless and unlikely to be correct.
Add to that the fact that ráibéad is an incredibly obscure word, which is not mentioned in Dinneen’s dictionary, though it is mentioned in Ó Dónaill’s. I have certainly never heard it in use. Because of this I don’t know how someone would use it, but I would assume from the definition that it is one of those words like pánaí (a word I do use) which just means something large. If it is like pánaí, then it is neither particularly flattering nor offensive. It’s just a fairly neutral comment about the size of something or someone.
In other words, it doesn’t sound to me like a suitable basis for a gang-name and certainly, Cassidy had no evidence of any connection with Irish beyond his misplaced faith in his own crazy revelations.
Speaking of which, if you are still in any doubt that Cassidy was a nut, check out this link, where he tries to persuade a group of people that the Ku Klux Klan derives its name from a Gaelic term meaning Cloaked Champions of the Clan. This one didn’t make it to the book, of course.