§ Akallabêth The Silmarillion

Thus the years passed, and while Middle-earth went backward and light and wisdom faded, the Dúnedain dwelt under the protection of the Valar and in the friendship of the Eldar, and they increased in stature both of mind and body. For though this people used still their own speech, their kings and lords knew and spoke also the Elven tongue, which they had learned in the days of their alliance, and thus they held converse still with the Eldar, whether of Eressëa or of the west-lands of Middle-earth. And the loremasters among them learned also the High Eldarin tongue of the Blessed Realm, in which much story and song was preserved from the beginning of the world; and they made letters and scrolls and books, and wrote in them many things of wisdom and wonder in the high tide of their realm, of which all is now forgot. So it came to pass that, beside their own names, all the lords of the Númenóreans had also Eldarin names; and the like with the cities and fair places that they founded in Númenor and on the shores of the Hither Lands.