Polite term for one's spouse's mother. Used both as a form of address and when referring to her in conversation.
お義母さんは料理がとても上手です。
My mother-in-law is very good at cooking.
お義母さん、これ、つまらないものですが。
Mother-in-law, this is just a little something for you.
Polite term for a woman who raises a child as her own, though not the biological mother. Less common than the mother-in-law sense.
彼女は幼い頃からお義母さんに育てられた。
She was raised by her foster mother from a young age.
Polite term for the wife of one's father who is not one's biological mother. Used in address and reference.
お義母さんとは最初はぎこちなかったけど、今は仲良しです。
At first things were awkward with my stepmother, but now we get along well.
Polite prefix お (o-) + 義母 (gibo, 'mother-in-law, foster mother, stepmother') + honorific suffix さん (-san). The reading おかあさん is a gikun (meaning-based reading) applied to the kanji 義母, using the familiar maternal address お母さん (okāsan) to convey warmth and respect.