Where does “undir” come from?

undir (Old Swedish) comes from Old Norse undir, from Proto-Germanic under, from Proto-Indo-European h₁entér, from Proto-Indo-European h₁en — in; in, inside.

Ancestry of “undir”, step by step

StepLanguageWordMeaning
1Old Norseundirunder, underneath
2Proto-Germanicunderamong, between; under, beneath; under
3Proto-Indo-Europeanh₁entérbetween
4Proto-Indo-Europeanh₁enin; in, inside
Every word from Proto-Indo-European h₁en →Every word from Proto-Indo-European h₁entér →Every word from Proto-Germanic under →