co-mother

Noun
(plural co-mothers)
- in polygamy, a wife of one's father who is not one's mother; that is, co-wife of one's mother
- in polygamy, the relationship between one co-wife and another, in respect to their children
- in a lesbian couple, the nonbirth mother (partner of the birth mother) of a child, especially one who takes an equal role in mothering the child
Origin
- com- + mother, as calque of Latin commater, French commère