Marc answered this one, not Maltz:

Actually, So'chIm is from a TNG episode (it's written "soh-chim" in the script). Worf asks Troi to be Alexander's So'chIm, which he describes as being Alexander's "surrogate mother" who'd take over being responsible for Alexander if anything were to happen to Worf. (Worf also says this would make Troi his stepsister, more or less.) The website Memory Alpha says a soh-chim is "most closely approximated" by stepsister/stepbrother (but I think that's not accurate — the soh-chim has a connection to the child, not the child's parents; I think the script has Worf and Troi talking about stepsister/stepbrother is so they could make a joke about Lwaxana Troi being Worf's stepmother) and is similar to the Human concept of "godparent" (though the word "godparent" is not in the script). Even though the only person we know about who is a soh-chim happens to be female, I think it's reasonable to assume that the individual chosen to be responsible for a child could be of any gender. So "godparent" is a good approximation. If a gender distinction has to be made, add loD or be' after So'chIm.

(qepHom 2020)