Where does “kaksoissisko” come from?

kaksoissisko (Finnish) comes from Finnish Sisko, from Finnish sisar, from Proto-Finnic sesar, from Proto-Balto-Slavic swésō, from Proto-Indo-European swésōr, from Proto-Indo-European su-h₁ésh₂-ōr, from Proto-Indo-European h₁ésh₂r̥ — blood.

Ancestry of “kaksoissisko”, step by step

StepLanguageWordMeaning
1FinnishSiskosister
2Finnishsisarsister
3Proto-Finnicsesarsister
4Proto-Balto-Slavicswésōsister
5Proto-Indo-Europeanswésōrsister
6Proto-Indo-Europeansu-h₁ésh₂-ōr—
7Proto-Indo-Europeanh₁ésh₂r̥blood
Every word from Proto-Indo-European h₁ésh₂r̥ →Every word from Proto-Indo-European su-h₁ésh₂-ōr →Every word from Proto-Indo-European swésōr →