Sibling-in-law
A relative by marriage through a sibling or spouse.
Wikipedia / Wikimedia Commons
A sibling-in-law is a person related by marriage through the spouse of one's sibling, the sibling of one's spouse, or the spouse of one's spouse's sibling. In Indian English, the spouse of one's sibling-in-law is specifically called a co-sibling (co-sister or co-brother). Siblings-in-law are connected by a type of kinship called affinity, meaning they are not related by blood.
- type
- Kinship relation
- category
- Affinity
- alternative_names
- Brother-in-law, sister-in-law, co-sibling, co-brother, co-sister
- legal_context
- Islamic law (Sharia) and Jewish law (halakha) prohibit sexual relations between siblings-in-law unless the spouse is no longer married
- cultural_note
- In Judaism, yibbum allowed a man to wed his deceased brother's childless widow
Lore & Background
Siblings-in-law are related by affinity, not by blood. The children of one's siblings-in-law are called nieces and nephews, optionally specified as 'by marriage' to distinguish from blood or adoptive relations. When one pair of siblings marries another pair of siblings, the siblings-in-law are doubly related—each through both a spouse and a sibling—and their children are double cousins.
Reader's Guide
The sibling-in-law relationship occupies a unique position between spousal and sibling bonds. One study found that relational closeness and satisfaction for all relationships in the triad of sibling, sibling-in-law, and spouse were correlated, and that the sibling-in-law relationship shared similarities with both spousal and sibling relationships. In religious legal systems such as Islamic law (Sharia) and Jewish law (halakha), sexual relations between siblings-in-law are considered incestuous unless the spouse is no longer married. In Judaism, the custom of yibbum provided a non-obligatory duty for a man to marry his deceased brother's childless widow to produce progeny. These rules and customs highlight the cultural and legal significance of the sibling-in-law bond, which balances familial closeness with social and religious boundaries.
Did You Know?
- In Indian English, the wife of one's sibling-in-law is called a co-sister, and the husband is called a co-brother.
- Children of one's siblings-in-law are called nieces and nephews, optionally specified as 'by marriage'.
- If one pair of siblings marries another pair of siblings, their children are double cousins.
- In Judaism, there was a custom called yibbum allowing a man to wed his deceased brother's childless widow.
Frequently Asked Questions
What is a sibling-in-law?
A sibling-in-law is a family member you gain through marriage rather than blood, specifically the spouse of your sibling, your spouse's sibling, or the spouse of your spouse's sibling. It is a broad umbrella term that covers what most people casually call a brother-in-law or sister-in-law.
Are siblings-in-law related by blood?
No. The bond between siblings-in-law is one of affinity, meaning it is created entirely through marriage rather than shared genetics. This sets them apart from biological siblings and other consanguineous relatives.
What does the term "co-sibling" mean in a family context?
In Indian English, co-sibling (or co-brother / co-sister) is the specific label for the spouse of one's sibling-in-law. It is a culturally rooted term that does not have a single direct equivalent in mainstream American English.
Do any religious or legal traditions restrict relationships between siblings-in-law?
Both Islamic law (Sharia) and Jewish law (halakha) forbid sexual relations between siblings-in-law as long as the marriage that created the bond is still in effect. Jewish tradition historically included an exception called yibbum, which allowed a man to wed his deceased brother's childless widow.
What kinship category does the sibling-in-law relationship belong to?
It falls under the affinity category of kinship, since the connection is established by marriage rather than by descent. Common alternative names for the relationship include brother-in-law, sister-in-law, co-sibling, co-brother, and co-sister.
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