Where does “sib-in-law” come from?

sib-in-law (English) comes from English SIB, from Middle English sib, from Old English sibb, from Proto-West Germanic sibbju, from Proto-Germanic sibjō, from Proto-Indo-European sebʰ-.

Ancestry of “sib-in-law”, step by step

sib-in-law traces back through two separate lines of ancestry.

via English SIB

StepLanguageWordMeaning
1EnglishSIBHaving kinship or relationship; related by same-bloodedness; kindred
2Middle Englishsibhaving kinship; kinsmen; peace
3Old Englishsibbkinship; peace
4Proto-West Germanicsibbjurelationship, kinship
5Proto-Germanicsibjōrelationship, kinship; friendship
6Proto-Indo-Europeansebʰ-

via English in-law

StepLanguageWordMeaning
1Englishin-lawA relative by marriage (or through affinity)
2English-in-lawRelated through marriage
3Englishmother-in-lawThe mother of one's spouse; A mother-in-law...
4Middle Englishmoder in lawemother-in-law
Every word from Proto-Indo-European sebʰ-Every word from Proto-Germanic sibjōEvery word from Proto-West Germanic sibbju