The Ornamental Dagger is only featured in 2004’s Alien vs Predator. The Celtic and Scar Predator both have this weapon. Celtic uses it against the Grid Alien but instead it is knocked out of his hand. Later in the film, Scar Predator uses the knife to cut into a dead alien to make a shield for Lex to use. He also fastens part of its tail onto the knife too. The Dagger does seem to be resistant to acid unlike the Predator’s wristblades and armour.
You can see some early concept art of the Dagger below from artists Joe Pepe and RK Post.