íta noun "a flash" (PM:363)
Primitive elvish
rus
root. brownish red
Quenya
íta
flash
íta
noun. flash, flash, *lightning
A noun for “a flash” appearing in The Shibboleth of Fëanor as part of a discussion the name Q. Itarillë, S. Idril from the late 1960s, derived from the root √IT (PM/363). It seems to be a bright and direct flash of light, as opposed to ᴹQ. tinde “glint” for a less brilliant and reflected flash of light.
Neo-Quenya: As a flash of light, this word might also be used for “✱lightning” and on this basis used for Neo-Quenya words having to do with electricity.
Sindarin
agol
noun. flash
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
Middle Primitive Elvish
rus
root. flash, glitter of metal
Gnomish
agla
noun. flash
A noun in the Gnomish Lexicon of the 1910s given as G. agla “flash” (GL/42); Tolkien made a point that it was not connected to G. augla “ray of sunlight, sunbeam” (GL/20), and thus it was likely derived from the early root ᴱ√KALA (QL/44). In the Gnomish Lexicon Slips it was revised from {aglan or agl >>} aglen “a flash” (PE13/108). In Early Noldorin Word-lists of the 1920s this became {aglen >>} ᴱN. aglann “ray of light” (PE13/136, 158).
Neo-Sindarin: I think this word can be adapted to Neo-Sindarin as ᴺS. agol “flash”, where the -ol is the usual result of a syllabified final l: ✱agl(a) > agḷ > agol. I would adapt the pre-revision Gnomish form because I think the Early Noldorin form is better as ᴺS. aglan “ray of light”, and agol also happens to compatible with early 1950s ✶ak’la- “shine out, flash” (PE18/87).
aglen
noun. flash
The root ᴹ√RUS “flash, glitter of metal” appeared in The Etymologies of the 1930s with derivatives ᴹQ. russe “corruscation, †sword-blade” and N. †rhoss “polished metal” where it served as the basis for the second element of the name Maidhros “Pale-glitter” or (Anglicanized) Maidros (Ety/RUS; MAD). In The Shibboleth of Fëanor from 1968, the second element of the names S. Maedros and S. Amros were explained as S. ross < ✶russā referring to their red-brown hair (PM/353, 366; VT41/10). A related etymological note stated:
> Common Eldarin (u)rus [was] used of a varying brownish red from what we should call brick-red to auburn. Hence Quenya, Telerin urus (stem urust-), Sindarin rust “copper”, rustui adj.; Quenya {ruska “red-brown”} rusko “a fox” (rusku-, pl. rusqui; ruskuite “foxy”). (calarus(t)- polished copper, lairus(t) verdigris). russe a head or pelt of red hair, russa red-haired. S. rusc fox, ross ([primitive] russā) red-haired, copper coloured, especially used of animals, as fox, red deer, and [?similar kind] (VT41/10).
This use of √(U)RUS as brownish-red is not entirely without precedent: in The Etymologies of the 1930s Tolkien gave the “root” (more likely just a primitive form) ᴹ√RUSKĀ with derivative N. rhosc “brown” (Ety/RUSKĀ), the basis for the name N. Rhosgobel “Brownhay” from Lord of the Ring drafts from the 1940s (TI/164), later translated as “russet village or ‘town’ (enclosure)” (RC/241). However in notes also associated with The Shibboleth of Fëanor, Tolkien gave the root √URUN = “copper” apparently as an extension of √RUN “red, glowing”, part of an explanation of the sobriquet of Nerdanel’s father: Q. Urundil “Copper-lover” (PM/366).
Neo-Eldarin: For purposes of Neo-Eldarin, I think it is best to assume 1930s ᴹ√RUS “flash, glitter of metal” was discarded in favor of 1968 √RUS “brownish red”. I’d also use √RUS as the basis for copper words rather than √URUN.