Nisroh

From Memory Alpha, the free Star Trek reference

The nisroh is a bladed weapon used by Tilonian merchants in the traditional bartering ceremony. In the ceremony, the merchant ceremonially wields the nisroh and is judged on his proficiency with the blade. Before his undercover assignment on Tilonus IV in 2369, Commander William T. Riker was briefed on the use of a nisroh by Worf, who accidentally cut him on the forehead. The wound became a focal point of the delusions manufactured by Riker's mind when he was resisting interrogation by the Tilonians. (TNG: "Frame of Mind")