Ilkorin

Ilkorin (plural Ilkorindi) is a Quenya word, literally meaning "not of Kôr". The Ilkorindi were a group of Elves from J. R. R. Tolkien's fictional universe. They first appear in The Book of Lost Tales. It was then a name with a broad meaning for all the Elves who "never saw the light of Kôr" and also for their many tongues. Kôr was the Quenya name for a hill and the city built on it, near the shores of the Bay of Faery.

Later, in the late 1920s, Tolkien applied the word only to those Elves (later called Sindar) who lived in Beleriand and were ruled by King Thingol:

"In the course of ages the tongues and dialects of Beleriand became altogether estranged from those of other Eldar in Valinor, through the learned in such lore may perceive that they were anciently sprung from Telerin. These were the Ilkorin speeches of Beleriand."

These Ilkorin Elves spoke three dialects:

Later on (in the early 1940s) Tolkien conceived the name Lemberin for that language, and said about Ilkorin that it "is not rightly a linguistic name, and included the Pereldar, and all who began the march, but did not come to Kór".

So Lemberin became the name for the tongue of the Telerin Elves that remained in Beleriand. Before the coming of the Noldor it was spoken far and wide in Beleriand (save in Ossiriand) and all the names of places, of rivers, woods, fields, plains, hills and mountains were given in this tongue.

...
Wikipedia