lǫngu

Forms of langr (“long”). The adverb more specifically is from the neuter dative singular.

lǫngu

1. long ago, long since

• Faroese: longu
• Norwegian Nynorsk: longe

lǫngu

1. inflection of langr:
   1. strong neuter dative singular positive degree
   2. weak feminine oblique singular
   3. weak plural nominative/accusative/genitive

lǫngu

1. inflection of langa:
   1. accusative singular
   2. dative singular
   3. genitive singular

• löngu in A Concise Dictionary of Old Icelandic, G. T. Zoëga, Clarendon Press, 1910, at Internet Archive.