A Sindarin-only root for “light; shine”, a variant of √KAL of the same meaning. Its most notable derivative is S. galad “radiance, light”, an element in the names Galadriel and Gil-galad. This root did not explicitly appear in the Qenya Lexicon of the 1910s, where the base for Qenya light words was given as ᴱ√KALA “shine golden” (QL/44), but nearly all the Gnomish derivations of this root begin with g-, as in G. gal- “to shine” and G. glarw(ed) “bright, light” (GL/39). Given that [[eq|initial [g] > [k]]] in early Quenya, this makes it very likely the actual early root was ✱ᴱ√GALA, or at the very least a blending of ᴱ√KALA and ᴱ√GALA.
The first explicit appearance of the root ᴹ√GAL “shine” was in The Etymologies of the 1930s (Ety/GAL), where it was given along with an extended root ᴹ√GALAN “bright” (EtyAC/GAL¹). Tolkien considered but rejected having some Quenya derivatives of these roots: ᴹQ. ala “day” and ᴹQ. alan “daytime” (EtyAC/GAL¹), but he seems to have decided that ᴹ√GAL was a Noldorin-only root, as described in the ᴹ√KAL entry from the same set of documents (Ety/KAL).
The root √GAL reappeared in various etymological notes from the 1950s and 60s, where Tolkien again iterated it was not used in Quenya, and was a root specific to Sindarin (PE17/59) and possibly also Nandorin (PE17/50). The root was potentially problematic in the name Gil-galad, however, in that it was not mutated to Gil-’alad. It seems likely that when Tolkien first coined this name, the second element was from N. calad “light” from the root ᴹ√KAL. This root and word survived into Sindarin (UT/65), and Tolkien sometimes still considered it the basis for Gil-galad (PE17/50).
However, at one point he decided the elements in the names Galadriel and Gil-galad were the same; to explain the lack of mutation in Gil-galad, he posited that the root was actually strengthened to √ÑGAL (PE17/59). Galadriel’s name in The Shibboleth of Fëanor from 1968 was based on the root √ÑAL “shine by reflection” (PM/347), so it seems this was the path Tolkien eventually followed. This makes the ultimate status of √GAL “shine” rather unclear, especially since some of its other derivatives like S. uial twilight (PE17/153) were sometimes derived from √ÑAL (PE17/169).
This root was the basis for words having to do with “light” for most of Tolkien’s life. Its derivatives include Q. cala “light” and S. aglar “glory” which likewise retained the same basic form and meaning throughout Tolkien’s life. The root ᴱ√KALA first appeared in the Qenya Lexicon of the 1910s glossed “shine golden” (QL/44) along with a rejected variant ᴱ√ALA “light” (QL/29). In this early iteration, the root ᴱ√KALA included a number of derivatives having to do with daytime, such as ᴱQ. kala “daytime (sunlight), 12 hours” and G. gala “daylight” (QL/44; GL/38). Also of interest is that most of the Gnomish derivatives from this period began with g-, indicating that the true form of the root may have been ✱ᴱ√GALA (or at least a blending with it), since [[eq|initial [g-] became [k-]]] in Early Qenya.
This G/K variation became explicit in The Etymologies of the 1930s, where ᴹ√KAL “shine” had a Noldorin-only variant ᴹ√GAL (Ety/GAL, KAL). Tolkien did consider having a few Quenya derivatives of ᴹ√GAL, but they were all rejected (EtyAC/GAL¹). In the 1930s, it also seems the “daytime” derivatives were transferred to ᴹ√AR “day” (Ety/AR¹). The root √KAL continued to appear in Tolkien’s later writings, variously glossed “shine”, “light” and “be bright”, with such frequency that it is impractical to list all the references. Likewise Tolkien continued to refer to the Sindarin-only variant √GAL on a regular basis; see that entry for details.
The root √KAL had a couple of extended forms of note, in particular √KALAR glossed “be radiant” in the 1930s (PE18/62), also appearing in the vowel-suppressed variant ᴹ√AKLA(R) “radiance, splendour” which served as the basis for Q. alcar/S. aglar “glory, brilliance, splendour, radiance” (PE17/105, 124; PE18/36, 87; VT47/13; Ety/AKLA-R, KALAR); in the Qenya Lexicon of the 1910s this variant root was given as ᴱ√ḶKḶ instead (QL/30). Tolkien frequently used the extension √KALAT as the representation of triconsontal roots (PE18/33, 86; WJ/392), though the only derivative he ever gave for it was ✶kalatta “a light, lamp” (PE21/80).