A word for “death” in The Etymologies of the 1930s under the root ᴹ√ÑGUR, where Tolkien said its personification was Mandos (Ety/ÑGUR). Tolkien also use this word as “death” in the phrase ᴹQ. núruhuine méne lumna “death-shadow on-us is-heavy” (LR/47, 56; SD/310).
Conceptual Development: A possible precursor to this word is ᴱQ. urdu “death” from the Qenya Lexicon of the 1910s under the early root ᴱ√GWṚÐṚ “die” (QL/104), given as a cognate to G. gurthu in the contemporaneous Gnomish Lexicon (GL/43). A variant of this form seems to have been briefly restored in Quenya prayers from the 1950s as incomplete urtulm..., probably Q. urtu with a possessive suffix, but this was quickly replaced by Q. fírië “death” (VT43/27, 34).
Neo-Quenya: For purposes of Neo-Quenya, I would use the word nuru for death as an abstract force or concept (Death), as opposed to the death of individuals which would be fírie (if natural or peaceful) or [ᴹQ.] qualme (if undesired or painful). This is the way its cognate [N.] guru was used (Ety/WAN).
A surname of Mandos as lord of the dead in Silmarillion drafts from the 1930s (LR/207). In The Etymologies it was given as a compound of nuru “death” and Fantur “Lord of Cloud”, the latter of which also appeared in the surname of his brother, Olofantur (Ety/ÑGUR, SPAN).
Conceptual Development: The first form of this name in the earliest Lost Tales was ᴱQ. Vefántur “Fantur of Death”, where the initial element ᴱQ. Vê was another name of Mandos (LT1/76; QL/37, 100). In early Silmarillion drafts from the 1930s this became ᴹQ. Nefantur (SM/166) and finally Nurufantur (LR/207). This name disappeared from Silmarillion revisions from the 1950s-60s, but the term Q. Fëanturi was still used to collectively describe Mandos and Lórien.