Blood oath

A blood oath is a vow among Klingons to take vengeance.

Kamarag once swore a blood oath against James T. Kirk for Kirk killing Kruge. 

In 2289, Curzon Dax swore a blood oath with Kang, Koloth and Kor to take revenge on the Albino after the Albino killed the children of the three Klingon captains. In 2370, Jadzia Dax stood by Curzon's blood oath when Koloth tracked down the Albino.