1.
mother-in-law
One's spouse's mother.
義母と同居している。
I live with my mother-in-law.
義母は料理が上手だ。
My mother-in-law is good at cooking.
義母との関係は良好です。
My relationship with my mother-in-law is good.
2.
stepmother
A woman married to one's father who is not one's biological mother.
TERMS OF ADDRESS:
While 義母 is the formal/written term, in conversation people typically address their mother-in-law as:
- お義母さん - most common
- 義のお母さん - explicit "in-law's mother"
CONTEXT:
義母 is more commonly used in:
- Written documents
- Speaking about (not to) one's mother-in-law
- Formal contexts
FAMILY TERMS WITH 義:
- 義父 - father-in-law
- 義兄 - brother-in-law (older)
- 義弟 - brother-in-law (younger)
- 義姉 - sister-in-law (older)
- 義妹 - sister-in-law (younger)
- 義理の息子 - son-in-law
- 義理の娘 - daughter-in-law
NUANCE:
The 義 prefix indicates a family relationship through marriage rather than blood.