Soh-chim is a Klingon word which has no direct translation, but is most closely approximated by "step-sister/brother" or, to a lesser extent, "god-parent". This title is conferred upon a respected adult friend by a Klingon parent; it is legally binding and well-recognised in Klingon law. A soh-chim is usually named to secure a child's future well-being when his or her parent(s) go into battle and the odds are against returning.
In 2370, Worf asked Counselor Deanna Troi to be his son Alexander Rozhenko's soh-chim in case anything were to happen to him. She gladly accepted the role. (TNG: "Parallels")