Soh-chim is a Klingon word which has no direct translation, but is most closely approximated by "step-sister/brother" and similar to the Human concept of a "god-parent". A Klingon parent will bestow this title upon a respected adult friend who agrees secure their child's future well-being; usually when the child's parent(s) go into battle and the odds are against returning. This agreement is legally binding and is well-recognized in Klingon law.
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")