The modern English word “sister” comes from the Old English word “sweostor”, which itself is related to similar words in other Indo-European languages, including Old Norse “systir”.
Norse ‘syster’ is a related Scandinavian form but not the direct origin of modern English "sister."
Norse ‘storr’ means "big" or "great" and is unrelated.
The Sanskrit ‘sita’ means "furrow" and is unrelated.
