brunnen

From Middle High German brunne, from Old High German brunno, from Proto-West Germanic *brunnō, from Proto-Germanic *brunnô, whence also Old English burna, Old Norse brunnr; ultimately from Proto-Indo-European *bʰrun- (“a bubbling forth; a fountain, wellspring, source”). The form is Upper German, most Low and Central German dialects using Born (now poetic in the standard language). This southern origin also explains the vocalism; the expected form is Bronnen with -u- → -o- before a nasal geminate