A word for “air” or “sky” appearing Appendix E of The Lord of the Rings from older †wilya, serving as the name of tengwa #24 [n] (LotR/1123). It is clearly a derivative of the root ᴹ√WIL (Ety/WIL). It has an abnormal plural form wilyar with initial w- in the 1950s version of the Nieninquë poem in the phrase yan i wilyar antar miquelis “✱to whom the air gives kisses” (PE16/96).
Conceptual Development: The notion of the “lower air” as a region dates all the way back to the earliest Lost Tales, where the innermost layer of air was called ᴱQ. Vilna (LT1/65). However, in the Qenya Lexicon of the 1910s, the term was ᴱQ. Vilya “air (lower)” as a derivative of the early root ᴱ√VILI (QL/101). The word vilya “lower air” appeared English-Qenya Dictionary of the 1920s but was deleted (PE15/68), and this term appeared as both the singular “air” and plural “airs” in version of Nieninqe and its drafts circa 1930: yan/yar i vilya(r) anta miqilis “to whom the air(s) give kisses” (MC/215; PE16/90, 92).
In the Ambarkanta of the early 1930s, the lower air was {Wilwa >>} Vista (SM/236, 240 note #1), but it was Wilwa again in the earliest tales of Númenor from the 1930s (LR/12) and was ᴹQ. {vilwa >>} wilma in The Etymologies of the 1930s under the root ᴹ√WIL “fly, float in air” (Ety/WIL). Q. vilya “air, sky” in Appendix E seems to be the last iteration in this chain.
Neo-Quenya: For purposes of Neo-Quenya, I think vilya refers mainly to air as the region above the ground, as opposed to ᴹQ. vista “air (as a substance)”. You breath vista, but birds fly through vilya, and breezes flow through vilya like ripples in a lake.
vilya noun "air, sky", also name of tengwa #24. Older wilya. (Appendix E). Early "Qenya" has Vilya (changed from Vilna) "lower air" (LT1:273); also vilya "air" (MC:215)