Þorsteinn (Old Norse) comes from Old Norse Steinn, from Proto-Norse ᛊᛏᚨᛁᚾᚨᛉ, from Proto-Germanic stainaz, from Proto-Indo-European steyh₂-, from Proto-Indo-European steh₂- — to stand.
Ancestry of “Þorsteinn”, step by step
Þorsteinn traces back through two separate lines of ancestry.