A hypothetical root serving as the basis for Sindarin words like dîn “silence” and dínen “silent” (PE17/95, 98) and ᴹQ. lína- “be silent”. Tolkien’s use of the Sindarin words in The Lord of the Rings is rather inconsistent, reflecting shifting rules on the circumstances in which words mutated in Sindarin. In his Unfinished Index of The Lord of the Rings, he said these words were tîn and tínen (RC/551). Given the conflict this would have with the root √TIN “spark”, for purposes of Neo-Eldarin I think it is best to assume this root is √DIN.
Primitive elvish
tin
root. sparkle, spark, sparkle, spark, [ᴱ√] twinkle, [ᴹ√] emit slender (silver pale) beams
ti
pronoun. *that by you
tini
noun. spark
tin²
root. silence
din Reconstructed
root. silence
The root √TIN was connected to Elvish words for twinkle and sparkle for much of Tolkien’s life. The root first appeared as ᴱ√TINI “twinkle” in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. tintya- “sparkle” and ᴱQ. tinwe “star” (QL/92). The root also had derivatives in the contemporaneous Gnomish Lexicon such as G. tim “spark, gleam, (star)” and G. tintiltha- “twinkle” (GL/72). In The Etymologies of the 1930s he had the root ᴹ√TIN “sparkle, emit slender (silver pale) beams” with derivatives like ᴹQ. tin-/N. tinna- “glint” and ᴹQ. tinwe/N. tinw “spark, (small) star” (Ety/TIN). The root √TIN was mentioned regularly in his later writings with glosses like “spark” or “sparkle” (MR/388; PE17/22, 66).