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 noun in The Etymologies of the 1930s glossed “agony, death” derived from the root ᴹ√KWAL “die (in pain)” (Ety/KWAL). In the contemporaneous version of Tengwesta Qenderinwa (TQ1) it was glossed “process of death, death agony” (PE18/58).
Conceptual Development: In the Qenya Lexicon of the 1910s it was ᴱQ. {qalma >>} qalme “death” with archaic variant †qalume, both under the early root ᴱ√QALA “die” (QL/76). In the contemporaneous Poetic and Mythological Words of Eldarissa it was simply qalme “death” (PME/76), but in Early Qenya Word-lists of the 1920s it was glossed “agony” (PE16/144).
Neo-Quenya: For purposes of Neo-Quenya, I would use this word primarily for “death”, but only for painful or unwanted death as opposed to natural or peaceful death, which is fírië (MR/250). The word qualme is most specifically applied to the (painful) process of death, and by extrapolation to pain so great that one feels as if they are dying: nán qualmesse “I am in death agony (actual or figurative)”.