A river in Gondor appearing on the maps of The Lord of the Rings (LotR/1186). In his discussion of the The Rivers and Beacon-hills of Gondor, Tolkien indicated this name was a collective noun or adjectival formation meaning “shingle, pebble bank” (VT42/11).
Conceptual Development: In Lord of the Rings drafts from the 1940s, the name N. Serni appears in a list of rivers (TI/312, WR/436).
A noun for a “shingle, pebble bank” in The Rivers and Beacon-hills of Gondor from the late 1960s from primitive ✶sarniye, the basis for the river name S. Serni (VT42/11). Here the gloss “shingle” is used in the sense of a mass of smell pebbles rather than as a roofing tile. This word is an unusual example of a final -i in Sindarin, because the i was protected by the final e that was itself lost. Tolkien indicated it might instead be an adjective formation (“pebbly”?) from the (rare) adjective suffix -i derived from primitive ✶-īya, -ēya (VT42/10-11).