The ceremonial knife with which a Klingon kills a dishonoured brother in the Mauk-to-Vor rite, used by Worf to stab Kurn aboard Deep Space 9.
The mevak is a short ritual dagger used in Mauk-to-Vor, the Klingon ceremony in which a warrior who has lost his honour asks a kinsman to kill him so that he may enter Sto-vo-kor. It appears in the Deep Space Nine episode Sons of Mogh.
After Worf refuses to support the invasion of Cardassia, Gowron strips the House of Mogh of its lands and titles. Worf's brother Kurn arrives on the station and asks for Mauk-to-Vor. Amid incense and chanting, Worf drives the mevak into Kurn's chest.
Dax and Odo interrupt and Bashir saves Kurn's life. Sisko, furious, forbids any second attempt, and Kurn is eventually given a new identity with his memory erased.