The usual Sindarin word for “snow” (Let/278; PE17/161; RGEO/62), especially fallen and long-lying snow (VT42/18), derived from primitive ✶lossē (PE17/161) based on the root √(G)LOS (PE17/26; RGEO/62). It sometimes appeared in a shorter form los (PE17/26, 161). See the entry on [s] for a discussion of these long vs. short variations; for purposes of Neo-Sindarin loss is probably preferable.
Conceptual Development: Perhaps the earliest iteration of this word was G. glui “snow” from the Gnomish Lexicon of the 1910s, likely related to nearby words like G. gloss “white” (GL/40). In The Etymologies of the 1930s, N. gloss from the root ᴹ√GOLOS was both noun “snow” and adjective “snow-white” (Ety/GOLÓS), but in later writing Tolkien split these into S loss “snow” (see above) and S. gloss “(dazzling) white” (RGEO/62; VT42/18).
A word for “snowy” mentioned in passing in The Road Goes Ever On, adjectival form of S. loss “snow” (RGEO/62).