Sindarin
ninniach
noun. rainbow
eiliant
noun. rainbow
ninniach
noun. rainbow
cirith ninniach
place name. Rainbow Cleft
The pass that led Tuor to the sea, translated “Rainbow Cleft” (S/238). This name is a combination of cirith “cleft” and ninniach “rainbow”.
Conceptual Development: In the earliest Lost Tales, this pass was first called G. Cris a Teld Quing Ilon “Gully of the Rainbow Roof” (LT2A/Teld Quing Ilon), revised to G. Cris Ilbranteloth (same translation) in the narratives (LT2/150, 202). In Silmarillion drafts from the 1930s, the name was changed again to N. Cris-Ilfing >> Cirith Helvin “Rainbow Cleft” (SM/141, 146). The name Cirith Ninniach emerged in Silmarillion revisions from the 1950s-60s (WJ/256, 299).
eilian
rainbow
eilian (pl. eiliain). Archaic elianw (so the coll. pl. may be eilianwath).
eilian
rainbow
1) eilian (pl. eiliain). Archaic elianw, hence maybe coll. pl. eilianwath. 2) ninniach (pl. ninniaich). The word appears to mean *”slender-crossing”.
eilian
rainbow
(pl. eiliain). Archaic elianw (so the coll. pl. may be eilianwath).
ninniach
rainbow
(pl. ninniaich). The word appears to mean ✱”slender-crossing”.
cû
noun. bow, bow; [N.] arch, crescent; [G.] waxing or waning moon
cû
bow
(i gû, o chû) (arch, crescent), pl. cui (i chui)
peng
bow
(i beng, o pheng), pl. ping (i phing)
A noun for “rainbow” in the name Cirith Ninniach “Rainbow Cleft” (S/238). Ninniach “rainbow” is perhaps a combination of the S. nîn “watery” and S. iach “ford”, perhaps a metaphorical ford of water across the sky. The long nn in the initial element ninn- is tricky to explain, but might be an example of an exchange of a long vowel īn with a long consonant inn; hat-tip to Elaran for this suggestion.
Conceptual Development: The name Cirith Ninniach (and hence the word for “rainbow”) went through quite a few changes. The earliest iteration of the name was G. Cris a Teld Quing Ilon “Gully of the Rainbow Roof” (PE15/21) so that quing ilon “✱bow of heaven” was “rainbow”, but this was quickly revised to G. Cris Ilbranteloth which was the form used in the early narratives (LT2/150, 202). G. ilbrant “rainbow” appeared in the Gnomish Lexicon of the 1910s with variant ilvrant (GL/50). By popular etymology, this was connected to G. brant “bow”, but that was not correct (GL/24). The second element was actually G. rantha “bridge” (GL/65), and the b came from its initial element G. ilbar “heaven[s]” (GL/50), so it literally meant “✱heaven-bridge”.
In Silmarillion drafts from the 1930s, the name of the pass was changed to N. Cris-Ilfing >> Cirith Helvin “Rainbow Cleft” (SM/141, 146). Both ilfing and helvin have unclear etymologies, but they are probably early iterations of N. eilian(w) “rainbow, (lit.) sky-bridge” from The Etymologies of the 1930s, a combination of ᴹ√ƷEL “sky” with N. ianw “bridge” (Ety/ƷEL, YAT), with variant elianw (EtyAC/YAT). Cirith Ninniach “Rainbow Cleft” emerged in Silmarillion revisions from the 1950s-60s (WJ/256, 299).
Neo-Sindarin: Noldorin eilian(w) “sky-bridge” might be adapted into Neo-Sindarin as ᴺS. eiliant using later S. iant for “bridge”, as suggested in HSD (HSD), but I see no reason not to just use attested S. ninniach for “rainbow”.