The land between river Gelion and the Blue Mountains translated “Land beyond Gelion” (S/124), a combination of thar “across” and the river name Gelion (SA/thar, PE17/34).
Conceptual Development: In Silmarillion drafts from the 1930s, the name first appeared as N. Targelion >> Thargelion (LR/265, 268), and also in The Etymologies with the same derivation as given above (Ety/THAR). In Silmarillion revisions from the 1950s-60s, Tolkien also considered the forms Thargelian (WJ/320) and Thorewilan (WJ/336).
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.