This page contains information regarding Star Trek: Picard, and thus may contain spoilers.
A qalankhkai (plural qalankhkan) was a Romulan Qowat Milat warrior who chose to serve as a "freeblade", binding her sword to a singular cause that she had judged worthy. Their criterion for worthiness was that it be a "lost cause".
As of 2399, half the Qowat Milat sisters on Vashti served as qalankhkan, attempting to keep the peace by patrolling roads and waterways, helping travelers, and defending Romulan and Terran lives. That year, Elnor chose to bind himself to Jean-Luc Picard as a qalankhkai, to assist him on his mission to find and protect Soji Asha. (PIC: "Absolute Candor")