A river in Gondor. It seems to be a combination of er “one” with the adjective suffix -ui, but in notes on The Rivers and Beacon-hills of Gondor Tolkien stated that: “it cannot be used for ‘first’ ... er was not used in counting series: it meant ‘one, single, alone’” (VT42/10). Tolkien further indicated it was not the usual adjective for “alone”, which was ereb, but it nevertheless got its name because it was short and swift and the only major Gondorian river without a tributary. Perhaps it was a pseudo-Sindarin name, assembled by less knowledgable Gondorians like the region name Arnen.

Conceptual Development: In Lord of the Rings drafts from the 1940s, this name first appeared as N. Ereg “First” (TI/312, WR/436).

Earlier name for the river S. Erui from Lord of the Rings drafts from the 1940s, apparently a Noldorin word meaning ereg² “first” (TI/312, WR/436).