A great river in eastern Beleriand (S/54). The meaning of the name is unclear. Given the river’s location in Ossiriand, this name might be Nandorin instead.
Conceptual Development: The name N. Gelion first appeared in Silmarillion drafts from the early 1930s as a revision of earlier Flend (SM/135). In The Etymologies, Tolkien said the name was based on the Ilkorin word gelion “bright” (Ety/GYEL). In later notes, Tolkien considered renaming the river to Gelduin >> Gevilon >> Gevelon or Gevolon, the last of these an adaptation of Khuzdul Gabilân “Great River” (WJ/336; NM/311). He did not apply this change in the Silmarillion revisions from the 1950s-60s, however.