See also dîn.1 for a discussion regarding this word
Sindarin
tîn
noun. spark, sparkle, twinkle of stars
tîn
adjective. his
tîn
adjective. silent, quiet
tîn
spark
n. spark, star. Q. tinwe spark (Poet. star).
tîn
adjective. silent, quiet
tîn
pronoun. his
Non-lenited form suggested by Carl Hostetter (VT31/21).
dîn
noun. silence; silent, quiet
A word for “silence” appearing in names like Amon Dîn “Silent Hill, (lit.) ✱Hill of Silence” (LotR/747; PE17/95) and Taur-na-Chardhîn “Forest of Southern Silence” (WJ/185). As originally conceived, it was probably based on an (unattested) root ✱√DIN as indicated by ᴹQ. lína- “be silent” from the late 1940s (PE23/76 note #19).
Conceptual Development: Tolkien’s use of this noun and its associated adjective dínen “silent” was inconsistent. The adjective should have been mutated in names like Rath Dínen “Silent Street”, but it remained unchanged (LotR/826). This may reflect Tolkien’s original reluctance to use dh in names while writing The Lord of the Rings. To reconcile these inconsistencies, Tolkien said in his Unfinished Index to The Lord of the Rings that the proper form of these words was tîn and tínen and both of these were adjectives meaning “silent” or “quiet” (RC/551).
Neo-Sindarin: For purposes of Neo-Sindarin, I would stick to noun dîn “silence” and adjective dínen “silent” to avoid conflicts with √TIN “spark”.
A word for “spark, sparkle, twinkle of stars” appearing as an element in S. ithildin “moon-star” (PE17/39, 66). Tolkien sometimes gave it the form tĭn (PE17/39) and sometimes tîn (PE17/66). It was derived from the root √TIN “sparkle, spark” (PE17/66). Primitive ✶tĭnĭ “spark” from Common Eldarin: Noun Structure of the early 1950s may be its ancient form (PE21/80).
In one place Tolkien gave the form tim “spark” as another name for (apparent) stars, but its final m is hard to explain (MR/388; PE17/22). In notes associated with The Shibboleth of Fëanor from 1968 Tolkien said “In the Northern dialect, however, in final position only, C.E. tw > dw, dw > ðw, thw > þw, nw became b, v, f, m” (VT41/8). Thus, tim may be the North Sindarin equivalent of Q. tinwë. However, in the document where it appeared, tim was clearly marked “S” for Sindarin. This form could also be a remnant of Gnomish or Ilkorin tim (see below).
Conceptual Development: The earliest precursor of this word was G. tim “spark, gleam, (star)” in the Gnomish Lexicon of 1910s, derived from the early root ᴱ√tin- (GL/70), cognate to ᴱQ. tinwe (QL/92). In the Gnomish period, [[g|final [nw] became [m]]], as discussed by Roman Rausch in his Historical Phonology of Goldogrin (HGP/§2.7). This was not true later, since in The Etymologies of the 1930s, N. tinw “spark, small star” was the cognate for ᴹQ. tinwe and the form tim was Ilkorin, all of these under the root ᴹ√TIN “sparkle” (Ety/TIN). In his later writings, Tolkien had the forms tin, tîn and tim, as noted above. Thus while the root and basic meaning of this word were quite stable, its form went through a number of variations.
Neo-Sindarin: For purposes of Neo-Sindarin, I’d use the form tîn since short vowels generally lengthened in monosyllables. I think properly it has the meaning “spark(le)” but metaphorically can apply to stars. For the ordinary word for “star”, I’d use gil.