For some time now, some of my on-line friends have advised me to provide a version of CassidySlangScam without the invective aimed at Cassidy and his supporters. In response to that advice, I am working on providing a glossary of the terms in Cassidy’s ludicrous book How The Irish Invented Slang with a short, simple and business-like explanation of why Cassidy’s version is wrong.
Cassidy claims that nan comes from the Irish word nain or naing for grandmother. In fact this is an English expression for “children’s nurse,” 1795, from the widespread child’s word for “female adult other than mother” (compare Greek nanna “aunt”), perhaps also influenced by a pet-name for Anne. As Cassidy says, there are words like nain and naing given by Dinneen in his dictionary, but they are not defined as “grandmother”. Dinneen says that it means a fostermother, while naing mhór means a grandmother (O’N.); he also adds the note “cf. Nanny and Nain, used for grandmother.”
The reference to O’N means the manuscript dictionary of Tadhg Ó Neachtain, which was written in the year 1739. In other words, this is earlier by several generations than the earliest reference to nanny meaning a nurse or grandmother in English.
In other words, this is interesting and worth investigating. However, it is also worth noting that Cassidy didn’t carry out any meaningful research on this word. He merely noted that there is a word nain meaning a foster-mother or a grandmother in Irish and asserted that this was the origin of the English term but without making any attempt to identify where this word came from or whether there were other candidates. And while the Ó Neachtain reference is early and interesting, there is not much other evidence for the word in Irish. It’s not in the Electronic Dictionary of the Irish Language. Furthermore, it occurs in other languages. For example, in Welsh, nain is the usual north Wales version of the word for grandmother, and it dates back to the 14th century.
Personally, I doubt whether the Irish term is the origin of the English expression but it is certainly worth looking at in greater depth.