Esgalduin was a major tributary of the Sirion, which rose in the dark heights of the Ered Gorgoroth from the Shadowy Spring, and flowed southwestward to meet the Sirion on the western borders of Doriath. It marked the boundary between the forests of Neldoreth and Region.
In the earlier Etymologies, the name Esgalduin was said to be Ilkorin for "River under Veil (of [?leaves])", consisting of the elements esgal ("screen, hiding, roof of leaves") + duin ("water, river").
- J.R.R. Tolkien, "Words, Phrases and Passages in Various Tongues in The Lord of the Rings", in Parma Eldalamberon XVII (edited by Christopher Gilson), pp. 15, 184
- J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings, Part Three: "The Etymologies", pp. 355 (DUI-), 357, (EZGE-), 386 (SKAL1-)