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| David and Jonathan became brothers-in-law when David married Jonathan's sister Mary Anne | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Asibling-in-law is thespouse of one'ssibling, the sibling of one’s spouse, or the spouse of one's spouse's sibling. InIndian English the latter can be referred to as a co-sibling (specifically a co-sister, for the wife of one's sibling-in-law,[1] or co-brother, for the husband of one's sibling-in-law[2]).
More commonly, a sibling-in-law is referred to as abrother-in-law for a male sibling-in-law and asister-in-law for a female sibling-in-law.
Siblings-in-law are related by a type ofkinship calledaffinity like all in-law relationships. All of these are relations which do not relate to the person directly by blood.[3]
Just like the children of one's siblings, the children of one's siblings-in-law are called simplynieces andnephews – if necessary, specified whether "by marriage", as opposed to "by blood" or "by adoption".
If one pair of siblings is married to another pair of siblings, the siblings-in-law are thus doubly related, each of the four both through one's spouse and through one's sibling, while the children of the two couples aredouble cousins.
One study, examining the issue of envy in the triadic system of sibling, sibling-in-law and spouse, concluded that "The sibling-in-law relationship shared similarities with bothspousal andsibling relationships" and that "Relational closeness and satisfaction for all relationships in the triad were correlated."[4]
InIslamic law (Sharia)[5] andJewish law (halakha),[6] sexual relations between siblings-in-law are prohibited as incestuous, unless the spouse is no longer married. Conversely, in Judaism there was the custom ofyibbum, whereby a man had a non-obligatory duty to wed his deceased brother's childless widow, so she might have progeny by him.[7]
