A small river flowing south out of the Ered Wethrin appearing in the Silmarillion revisions from the 1950s-60s and associated maps (WJ/181, 261) but not in the published version of The Silmarillion. The final element is likely the lenited form of sîr “river”, and the initial element might be lith “ash” (as suggested by David Salo, GS/383).
place name. ?Ash River
Word Gloss lith “ash, ash; [N.] sand” sîr “river, stream”