name. Nightingale, (lit.) Daughter of Twilight
The name that Beren gave to Lúthien, translated “Nightingale”, more literally “Daughter of Twilight” (S/165), a derivation of the primitive form ✶Tindōmiselde (PE19/73). It is essentially a combination of tinnu “twilight” and the suffix -iel¹, except that the archaic final -v lost in tinnu was preserved in the compound.
Conceptual Development: This name first appeared as Tynwfiel in the earliest Lost Tales, probably a Welsh-like spelling of the name (LT2/41), but the normal spelling G. Tinúviel emerged in the Lays of Beleriand from the 1920s and so remained thereafter (LB/22). In the Etymologies from the 1930s, N. Tinúviel had the same derivation as given above (Ety/SEL-D, TIN).
1) dúlinn (i dhúlinn) (dusk-singer), same form pl. except with article (i núlinn) (SD:302). 2) merilin (i verilin), no distinct pl. form except with article (i merilin), coll. pl. merilinnath. Suggested Sindarin form of ”Noldorin” ”moerilind” = mörilind. 3) tinúviel (”daughter of twilight”, a poetic kenning) (i dinúviel, o thinúviel), pl. ?tinúvil (i thinúvil), coll. pl. tinúviellath (MR:373, WJ:62)