The Knife looks like an ordinary fancy butterknife suitable for use in fine dining, except for being scaled up in size to where it's four feet long.
Part of a set of three utensils (The Spoon, the Knife, and the Fork), it is said to have the power to open and close gateways between universes, and to do great damage to Outsider creatures.
It is believed to originate in the time of the Pre-Logrus civilization, one of the more unusual artifacts to survive the War of the Gods. It, the Spoon, and the Fork, were all made by Wayland Smith, supposedly.
Long held by the Elder Gods in Kadath, they have passed it on to Kanna, Lian, Touga, and Thoric, after they helped end the siege of Kadath. Generally carried by Kanna, though she has loaned it to Ruka and Moriya in the past.