The horse of Glorfindel (LotR/213). In Tolkien’s notes on Words, Phrases and Passages from the Lord of the Rings from the late 1950s or early 1960s, he translated this name as “Sunlit Foam”, a compound of ast “light or heat of the sun” and faloth “large foamy wave” (PE17/18). He immediately rejected this etymology, stating that “Q. áze is from √GAS”, so that its Sindarin cognate would be ✱gast, not ast.
Elsewhere, however, Tolkien derived Q. árë “sunlight” < áze < √AS “warmth” (PE17/145, 148; VT43/18). If this is the correct root instead of √GAS, perhaps S. ast (and the translation of the name of Asfaloth) could be considered valid as well.
Conceptual Development: When this name first appeared Lord of the Rings drafts from the 1940s, it was already in the form N. Asfaloth (RS/368).
_prop.n. _lit. 'Sunlit foam', name of a white horse. The original meaning is uncertain. >> ast, faloth