The Sindarin name of the river “Greyflood” translated on the map of The Lord of the Rings (LotR/1082). This name is a combination of gwath “shadow” and l(h)ô “flood” (UT/263).
Conceptual Development: This name first appeared as N. Gwathlo with a short o on the draft maps of the Lord of the Rings from the 1940s (TI/304, 312).
gwath (“shade, shadow, dim light”) + lô (“shallow lake, fenland”)