Meaning 'single-mountain', this is the Sindarin form of Lonely Mountain, as used in the records of Gondor and the Reunited Kingdom.

The term Erebor does not appear in The Hobbit, but is first used in The Lord of the Rings, by Aragorn during the captains' debate following the Battle of the Pelennor Fields.

In Appendix A Durin's Folk Tolkien uses Erebor throughout, and this remains the name for the Lonely Mountain thereafter.
Encyclopedia entry originally written by cirdaneth