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When the Gnomes came to the Great Lands with Fëanor, they intermingled with the Ilkorindi, the Dark Elves, and their languages, Kornoldorin and Ilkorin respectively, were likewise mingled. This was the origin of Noldorin.
 External history
A Celtic-sounding language spoken by the Gnomes/Noldoli existed since the beginning of Tolkien's mythology. In its first stages it was called Gnomish and resembled the later Noldorin/Sindarin despite noticeable differences.
The evolution of the language continued over several years. During the 1930s it was known as Noldorin, and gained a greater similarity to the Sindarin of The Lord of the Rings. This version of the language appears in the Etymologies.
Noldorin was the existing version of the language during the writing of The Lord of the Rings. The Elvish phrases in The Lord of the Rings, now known as Sindarin, were "Noldorin" in Tolkien's mind throughout the writing process. It was only while compiling the Appendices that he decided to rewrite the language's backstory and change the name to Sindarin.
Tolkien consulted the Noldorin language of the Etymologies extensively in his work on Sindarin, adapting old words to fit his new version of the language. This same method of adapting Noldorin words to create Sindarin equivalents is used by modern students of Elvish. The resulting vocabulary is typically referred to as "Neo-Sindarin" to distinguish it from attested Sindarin.
 An Example of Noldorin to Sindarin Adaption
The Old Noldorin initial l-/r- became lh-/rh- in Noldorin. In Sindarin, however, they remain the same. The Old Noldorin diphthong ai becomes oe in Noldorin, but ae in Sindarin.
According to the Etymologies, the Old Noldorin word raika evolved into Noldorin rhoeg. A modern student of Elvish would update this word to the Neo-Sindarin *r
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings, "Part Two: Valinor and Middle-earth before The Lord of the Rings, V. The Lhammas" p.177
- ↑ J.R.R. Tolkien, "Early Qenya and The Valmaric Script", in Parma Eldalamberon XIV (edited by Carl F. Hostetter, Christopher Gilson, Arden R. Smith, Patrick H. Wynne, and Bill Welden) p.61-62