Tolkien’s Elvish words for “gold” were fairly stable in his conception of the languages, resembling Q. laurë and S. glaur for most of his life. The main exception was the Early Noldorin and Gnomish forms of the 1910s and 20s, which were ᴱN./G. glôr (PE13/144; GL/40). These early forms survived to some degree in Tolkien’s later conceptions, because in Sindarin compounds au often reduced to o, and thus the name Glorfindel “Golden-hair” retained the same form and meaning for Tolkien’s entire life despite the revision of G. glôr >> S. glaur.
Tolkien’s first primitive root for these words was ᴱ√LOU̯RI in the Qenya Lexicon of the 1910s (QL/51). This reflected the Early Qenya sound change whereby [[eq|[ei], [ou] became [ai], [au]]]; later on these ancient diphthongs usually became [ī], [ū]. In this earliest conception, the root and its derivatives referred to the physical substance of “gold”, though not quite its mundane nature: Tolkien said that ᴱQ. laure was the “mystical” or “magic” name of gold as opposed to its more mundane name ᴱQ. kulu (QL/42; LT1/100).
Tolkien introduced a new root ᴹ√GLAWAR or ᴹ√LAWAR for these words in The Etymologies of the 1930s, along with the modified form for its Noldorin derivative N. glaur (Ety/GLAW(-R), LÁWAR). Tolkien said that ᴹ✶laurē referred to the “light of the golden tree Laurelin” (Ety/LÁWAR), indicating a conceptual shift in the meaning of the root to “golden light or colour” rather than “mystical gold”. Indeed, in etymological notes Tolkien wrote sometime around 1960, Tolkien said of √LAWAR: “The application to gold of this stem was poetic and referred to colour primarily ... not to material (malta)” (PE17/159).
Tolkien’s representation of this root as both √GLAWAR and √LAWAR indicates some uncertainty on whether the initial gl- was from Common Eldarin or was only a later Ancient Telerin innovation. However, in later writings Tolkien typically represented the primitive word as ✶glawar(e) (PE17/17; PE21/80; VT41/10), and in the Outline of Phonology from the early 1950s Tolkien gave the Ancient Quenya word AQ. alaurē “sheen of gold” whose vowel augment arose from an abnormal vocalization of the ancient spirantalized initial g-: ✱glawarē > glaurē > ʒlaurē > alaurē (PE19/79). This strongly indicates the primitive root was √GLAWAR.
This root was variously connected to life and warmth throughout Tolkien’s life. The earliest iteration of the root was ᴱ√LAWA from the Qenya Lexicon of the 1910s whose meaning was described as “much same as KOẎO [have life], but used of a vegetable”; it had derivatives like ᴱQ. laule “life, mode of life”, ᴱQ. laute “living thing, (esp.) vegetable”, and ᴱQ. lauke “vegetable, plant (species)” (QL/52). In the contemporaneous Gnomish Lexicon it had derivatives like G. lauth “a plant, herb” and G. laug “(of plants) alive, having sap, green, vigorous” (GL/53).
In The Etymologies of the 1930s it was glossed “warm” with derivatives ᴹQ. lauka and N. lhaug of the same meaning (Ety/LAW). In the Quenya Verbal System of the 1940s it was glossed “abound” with a Quenya verb ᴹQ. lauta- of the same meaning (PE22/103).
The root √LAW appeared in notes from the late 1950s serving as the basis for Q. loa “sun-year”, originally with the sense ✶lawā “growing, blooming”; it was also explicitly connected to its extended form √LAWAR with the sense “golden colour” (PE17/159). Its final appearance in currently published materials was in some Late Notes on Verbs from 1969, where it was given as √LAW “flourish (green), grow” with derivative Q. lauya- of the same meaning (PE22/156).
Despite all these minor variations, the general meaning of the root was fairly stable, having mainly to do with life and flourishing (especially of plants), and also connected to warmth and sunlight, probably by association with its extended form √(G)LAWAR “golden colour or light”, which applied to sunshine among other things.