Gnomish
aglen
noun. flash
agla
noun. flash
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
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).