Illuin place-name, name of one of the Lamps of the Valar; apparently incorporating the element luin "blue" (Silm): hence *"all-blue"?
Quenya
illuin
proper name. Illuin
Illuin
blue
luinë
blue
luinë adj. "blue", pl. luini (PE17:66, VT48:23, 24, 28, Nam, RGEO:66). Common Eldarin luini- would also be the stem-form in Quenya (VT48:24). Compare luinincë. Apparently -luin in Illuin, the name of one of the Lamps of the Valar (q.v.), Helluin, name of the star Sirius, and Luinil, name of another blue-shining star (or planet). (SA; Luinil is tentatively identified with Neptune, MR:435). Cf. also menelluin "sky-blue", used as noun = "cornflower" (J.R.R. Tolkien: Artist & Illustrator p. 193).
luinë
adjective. blue
lúnë
blue
lúnë (stem *lúni-, given the primitive form ¤lugni) adj. "blue" (LUG2, LT1:262; later sources rather give luinë, with pl. form luini_ in Namárië)_. According to VT45:29, lúnë in the Etymologies was changed by Tolkien from lúna.
ninwa
blue
ninwa adj. "blue" (LT1:262)
The northernmost of the two lamps that first lit the world (S/35). The meaning of this name is unclear.
Conceptual Development: In Silmarillion drafts from the 1930s, the name of this lamp was ᴹQ. Helkar (LR/32). In the 1950s, Tolkien changed this to Foros and then Forontë (both probably from the root ᴹ√PHOR “right hand, north”) before settling on Illuin (MR/7).