The basic Quenya word for “fire” derived from the root √NAR of the same meaning (PE17/29, 38), more specifically “fire as an element” or as a force or abstract concept (PE17/183), versus ruinë “a fire, a blaze” which is an individual fire or blaze in the physical world. In The Etymologies of the 1930s it appeared as ᴹQ. nár or náre “flame” derived from the root ᴹ√NAR “flame, fire” (Ety/NAR¹).
Conceptual Development: The Qenya Lexicon of the 1910s had as a derivative of the root ᴱ√SAH(Y)A “be hot” the word ᴱQ. Sā “Fire, especially in temples, etc. A mystic name identified with Holy Ghost” (QL/81), and this “mystic name” was also mentioned in the Poetic and Mythological Words of Eldarissa (PME/81). Thus it seems ᴱQ. sá was “mystic fire”, as opposed to ᴱQ. uru which was ordinary “fire” (QL/98).
Neo-Quenya: For purposes of Neo-Quenya, I would use this word as [ᴹQ.] náre as an independent word, and use nár or nar in compounds only. This helps keep it distinct from nár the plural of ná- “to be”.
nár noun "flame", also nárë (NAR1).Translated "fire" in some names, see Aicanár(o), Fëanáro (where nár apparently has the masculine ending -o added to it). According to PE17:183, nár- is "fire as an element" (a concrete fire or blaze is rather called a ruinë).