The female cousin or cousin-in-law of one’s parent.
A woman of an older generation than oneself, especially a friend of one's parents, by means of fictive kin.
The sister or sister-in-law of one’s parent.
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.