Thorn Sir

Thorn Sir ("Eagle-stream") was a river according to the early version of the legendarium in The Book of Lost Tales. It was located beneath Cristhorn, at the bottom of a gorge in the Encircling Mountains into which Glorfindel and the balrog fell. After this battle the river was stained black by the balrog's blood for many days. Its Qenya cognate was Eäsindi.

This river was later mentioned as Thornsir in an unfinished lay of Eärendel, but was not used by J.R.R. Tolkien in any other text.