Based on the Harry Potter Bellatrix Lestange dagger, the dagger that killed Dobby.
So a bit of Nerdy back story here. Aragorn (or Strider) was taken to Rivendell as a child after his father had a nasty encounter with some Orcs. He lived there for a time, seemingly becoming well antiquated with Steve Tylers music (and daughter)until he went and joined the Rangers. When he did so he took with him much of what he had learned from the elves including this knife. Oh and don't come down all hard on me cos I didn't get the story perfect, its my website and I will say what I want OK?
So you might remember that chap with the impossible sounding name 'Vin Deisel' who spends altogether too much time driving his cars in what can only be termed an anti-social manner, of and he did a couple of Sci=Fi movies (which do not make up for that stinker XXX) From the Movies 'Pitch Black' & 'The Chronicles of Riddick' comes the nifty blades that Riddick always carried to good effect.
The Demon-Killing Knife from Supernatural is an ancient knife that was created by the Kurds which possesses the power to permanently kill most demonic entities. In the hands of Sam and Dean Winchester, it is bad news for any demon they come across.