Grandmothers have a lot to answer for. My own Grandma's contribution to the language was to request that we pile the coal on the fire and "have a good blizzy" on a cold winter's night.

"Slitter" is not one I've ever come across, even from my half-Scottish wife, who uses her fair share of dialect words. I am wondering if your Grandmother would claim - along with the White Knight - that "It's my own invention" ?