godsib
One's sibling or kin via a godfamily tie: one's or one's child's godparent, or one's godchild's parent, or one's godparent's child.
historical
The fireplace also heated water for the godsibs to wash their hands with as they were instructed by the rubric to do before leaving the church.
Where it comes from
Learned borrowing from Middle English godsib; doublet of gossip; see those entries for more.
Adapted from the Wiktionary entry godsib (CC BY-SA 4.0).