Where does “sisterkins” come from?

sisterkins (English) comes from English sister, from Middle English suster, from Old English sweostor, from Proto-West Germanic *swester — sister.

Ancestry of “sisterkins”, step by step

sisterkins traces back through two separate lines of ancestry.

via English sister

StepLanguageWordMeaning
1EnglishsisterA daughter of the same parents as another person;...
2Middle EnglishsusterA sister or step-sister; a female sibling
3Old Englishsweostorsister
4Proto-West Germanic*swestersister

via English kins

StepLanguageWordMeaning
1Englishkinsplural of kin
Every word from Proto-West Germanic *swester
sisterkins — Etymology, Origin & Word History | Etymology Explorer