It may be a letter opener but my Grandma had something like that (less ornate) and she used it to crease paper after it had been folded. She worked in a book bindery for years and it was what they used on the pages of the books to really crease the paper fold. I also own a similar one (it's plastic) and use it when I make cards, I bought it at Stampin Up. Maybe it was used in quilting somehow? I use my plastic one when I am cutting fabric and need a good fold. The one pictured is beautiful.