Where does “syster” come from?

syster (Swedish) comes from Old Swedish systir, from Old Norse systir, from Proto-Norse ᛊᚹᛖᛊᛏᚨᚱ, from Proto-Germanic swestēr, from Proto-Indo-European swésōr, from Proto-Indo-European su-h₁ésh₂-ōr, from Proto-Indo-European h₁ésh₂r̥ — blood.

syster (Swedish): a sister; a nurse; a nun; a female member of a...