A lot of what we think of as American folk music snuck its way over here from the taverns of Ireland and farm lands of Scotland. I think it is interesting that in this genre of music there are two songs about a silver dagger and a tragic love story of disallowed marriage.
The more popular one is called "The Silver Dagger"
The other song, sometimes called "The Silver Dagger", is more commonly known as "Katie Dear". While similar, this one has more of the Romeo & Juliet feel to it.