My mother-in-law is very good at cooking.
A woman who raises a child not biologically her own, in a formal or legal fostering arrangement. Less common than the mother-in-law sense.
She was raised by her foster mother from a young age.
The wife of one's father who is not one's biological mother. Can be used in both legal and informal contexts.
At first things were awkward with my stepmother, but now we get along well.
I've been living with my mother-in-law since I got married.
My wife is always careful to be considerate toward her mother-in-law.
My husband's sister and I take turns caring for our mother-in-law.