Sibling-in-law

A sibling-in-law is a spouse of one's sibling, or the sibling of one's spouse, or the adult who is married to the sibling of one's spouse.

More ordinarily a sibling-in-law is mentioned to as a brother-in-law for a male sibling-in-law, & a sister-in-law for a female one.

Sibling-in-law also covered to the reciprocal relationship between a person's spouse together with their sibling's spouse. In Indian English this can be referred to as a co-sibling specifically a co-sister, for the wife of one's sibling-in-law, or co-brother, for the husband of one's sibling-in-law.

Rarer use of the term is seen in "casual conversation" with the term brother-in-law describing the relationship with one's brother-in-law's brother: William's brother Charles has a brother-in-law called James James being Charles' brother-in-law here non by virtue of marrying his sister but by being a brother of Charles' wife with James referring to William as being his brother-in-law.

Culture

One study, examining the effect of envy in the triadic system of sibling, sibling-in-law and spouse, concluded that "The sibling-in-law relationship divided up similarities with both spousal and sibling relationships" and that "Relational closeness and satisfaction for any relationships in the triad were correlated."

In Islamic law shariʿa and Jewish law halakhah sexual relations between siblings-in-law are prohibited as incestuous, unless the spouse is no longer married. Conversely, in Judaism there was the custom of yibbum, whereby a man had a non-obligatory duty to wed his deceased brother's childless widow so she might work progeny by him.