Quendi and Eldar
From Tolkien Gateway
Quendi and Eldar is a collection of short essays by J.R.R. Tolkien published in The War of the Jewels which provide the etymological development of certain words the Elves used to name themselves and other peoples, or to refer to individuals in some way.
The "Appendix D" was not published in The War of the Jewels, but was released years later in Vinyar Tengwar 39.
