Writing about the Irish? You might want to take a peak at this…
You can never have too much help digging up information about the topics on which you write. I enjoy finding these points and sharing them with readers because I not only find history fascinating, but I also work with history to create my novels. Authenticity requires understanding cultural nuances such as slang, and it’s hard, because slang is always changing. This also ignores how language adapts such words and erases their origin. That Irish words litter New York City slang isn’t surprising. The immigration of Irish during the famine was huge.
Irish words litter New York City slang – IrishCentral.com.

A sketch of the residents of Five Points, a famously Irish neighborhood in New York. Proving that American slang has its roots in the Irish American urban experience. Photo by: Secondat