What is my sister's mother-in-law to me?
Your sister's mother-in-law has no kinship title for you, because English never named this link. She is your sister's spouse's mother, so the marriage that ties her to your family is your sister's, not yours. People often reach for 'co-mother-in-law', but that title belongs to your parents, whose child married her child.
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Sister's mother-in-law
English has no word for this person. The marriage that links you is your relative's, not yours, so they aren't your in-law, and families just say “sister's mother-in-law”.
- You
- Your sister
- Her spouse
- Their mother
From the other side, you are their child-in-law's sibling.
This connection runs through a marriage, not a shared ancestor, so the ancestor chart can't draw it.
The calculator below works out blood relationships through a shared ancestor — use it to explore the rest of your tree.
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This relationship sits outside the shared-ancestor model, so the card above carries the answer and the calculator opens in its default state. Work out any blood relationship with it, or open the full relationship calculator.
Related questions
FAQs
Is my sister's mother-in-law my co-mother-in-law?+
No. Co-mother-in-law names a parent on the other side of your own child's marriage. She is your parents' co-mother-in-law, not yours.
What do I call my sister's mother-in-law?+
Most people say "my sister's mother-in-law" or use her first name. From her side you are her child-in-law's sibling, which has no name either.
Does the calculator store my family details?+
No — it runs entirely in your browser. Nothing you enter is uploaded or saved on our servers.
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