underground

underground · adjective, adverb, noun, verb¹

1. Proto-Indo-European*h₁én
2. Proto-Indo-European*h₁entér
3. Proto-Indo-European*h₂én
4. Proto-Indo-European*dʰeh₁-?
5. Proto-Indo-European*(H)n̥dʰí
6. Proto-Indo-European*(H)n̥dʰér
7. Proto-Germanic*under
8. Proto-West Germanic*undar
9. Old Englishunder
10. Middle Englishunder
11. Proto-Indo-European*gʰrem-
12. Proto-Germanic*grunduz
13. Proto-West Germanic*grundu
14. Old Englishgrund
15. Middle Englishgrounde
16. Middle Englishundergrounde
17. English todayunderground

From Middle English undergrounde (adverb), equivalent to under + ground or under- + ground. Compare Dutch ondergrond, ondergronds, German Untergrund, Danish undergrunds.

underground · verb²

See the etymology of the corresponding lemma form.