It is said also that these Men had long had dealings with the Dark Elves east of the mountains, and from them had learned much of their speech; and since all the languages of the Quendi were of one origin, the language of Bëor and his folk resembled the Elven-tongue in many words and devices. ~ The Silmarillion, Chapter 17 (The First Men by TurnerMohan, deviantART)
