xứ Nghệ (Vietnamese) comes from Vietnamese xứ, from French sou, from Latin solidus, from Proto-Italic soliðos, from Proto-Indo-European solh₂-i-dʰ-o-s, from Proto-Indo-European solh₂- — whole.
Ancestry of “xứ Nghệ”, step by step
xứ Nghệ traces back through two separate lines of ancestry.