The word is deduced from its mutated form, but it is worth mentioning that a stem GALÁN "bright", with glan "daylight" (and later "clear") as derivative, is listed in the Etymologies (not included in the published text, but see VT/45:13). Most of the words meaning "white" in the Indo-Eureopean languages come from the original notion of "brightness", e.g. Greek leukós "white" is cognate with Latin lucere "to shine", lux "light". This association of sense is also found in Gnomish, PE/11:39 (glan "clean, pure", from "bright" originally) and in Early Noldorin (PE/13:144, glann "clean"). The similarity with Welsh glan (where the vowel, incidentally, is also long, though this is concealed by Welsh orthographic convention) is also striking
Quenya
calima
bright
calima adj. "bright" (VT42:32); cf. ancalima; in PE17:56, arcalima appears as another superlative "brightest" (see ar- #2).