Reconstruction:Proto-West Germanic/dūnā

Etymology
and ; possibly from (whence also 🇨🇬), from  base, from. Unlike permanent hills, sand dunes are ever-shifting due to storms and wind, and are not optimal places to build fortifications. Alternatively, perhaps borrowed from, from the same Proto-Indo-European root above, which also developed the sense of "hill, fortified hill" in 🇨🇬; however phonology makes a borrowing from Brythonic untenable, as the vowel there shifted from ū to i giving 🇨🇬 where Germanic still clearly has ū.

Noun

 * 1)  sand dune
 * 2) hill