Ered: mountains. Luin: blue. The Blue Mountains, sometimes referred to as the Ered Lindon. The mountain range originally forming the boundary between Eriador and Beleriand, home of the Dwarf Kingdoms of Nogrod and Belegost.

In the destruction of Beleriand the Ered Luin became split by the Gulf of Lhun and the land between the mountains and the sea formerly parts of Thargelion and Ossiriand formed the elf kingdom of Lindon.

Part of the Dwarf Kingdoms also survived and continued as a Dwarf homeland throughout the Third Age.

Additional information from Potbellyhairyfoot and Cirdaneth