cha'DIch was a title in the Klingon legal system.
A warrior challenging a ruling of the Klingon High Council was not allowed personal combat. He therefore chose a cha'DIch to fight for him. The person selected as cha'DIch would speak the words "jIlajneS. ghIj qet jaghmeyjaj." ("I accept. May your enemies run with fear.") After being introduced to the council, the cha'DIch was handed a sword in a scabbard to wear.
Kurn served as his brother Worf's cha'DIch when Worf challenged the High Council in 2366. When Kurn was injured in an assassination attempt by Duras, Jean-Luc Picard became Worf's new cha'DIch. (TNG: "Sins of the Father")
William T. Riker compared Carol Freeman to being his cha'DIch during their younger years and reminisced about the times they got into trouble together, although Freeman apparently contended that she had been an active participant. (LD: "No Small Parts")