USEDN'T

I thought I'd been here long enough to hear at least most of the different way the Irish use the English language, but I came across a word this week that I have not really heard here yet. I just finished a book called, The New Policeman this week. It's by an Irish author and is set in Ireland. It is actually a children's book and has a lot of Irish culture in it. It has won a couple of awards. In this book, the characters use the word "usedn't". How would you even pronounce that? In the context, I took it to mean that someone had done something once, but now they didn't. I'll have to listen harder to see if anyone uses it.