A noun for a natural or peaceful death. This word originated with the death of Míriel, the first wife of Finwë, who choose to pass away after the difficult birth of their son Fëanor. As Tolkien described it:

For before the passing of Míriel the Eldar of Valinor had no word for “dying” in this manner, though they had words for being destroyed (in body) or being slain. But fírë meant to “expire”, as of one sighing or releasing a deep breath; and at the passing of Míriel she had sighed a great sigh, and then lay still; and those who stood by said fírië “she hath breathed forth”. This word the Eldar afterwards used of the death of Men (MR/250).

As such, this word was based on the verb fir-, originally meaning “breath forth”, but later also being used mainly in the sense of “to die (a nature death)”. Tolkien also used fírië as a noun for “death” in early versions of his Aia María prayer from the 1950s (VT43/34).

Conceptual Development: In the Qenya Lexicon of the 1910s Tolkien had ᴱQ. fé “last hour, death” based on the early root ᴱ√ǶEHE “breath; die, expire”, thus expressing a similar connection between the final breath and death (QL/41). In the contemporaneous Poetic and Mythological Words of Eldarissa, the word fē was in fact glossed “act of death, last breath” (PME/41). In The Etymologies of the 1930s Tolkien had ᴹQ. faire “natural death (as act)” also based on the root ᴹ√PHIR (Ety/PHIR).

Neo-Quenya: For purposes of Neo-Quenya, I’d stick with fírie for “(natural) death”, since in Tolkien’s later writing Q. fairë was used for a disembodied spirit. I would use fírie only for a peaceful death. For death by accident, murder or disease I’d use [ᴹQ.] qualme “death agony”.