Was Mount Erebor called “The Lonely Mountain” because it was the singular feature in the area, or for some other reason?

Question

Was Mount Erebor called "The Lonely Mountain" because it was the singular feature in the area, or for some other reason?

The map to The Lonely Mountain.

Answer 1

This map at http://www.monkeyinthecage.com/2012/11/05/top-five-reasons-to-be-excited-about-the-hobbit/ would seem to indicate that it is indeed by itself.

From memory of the book, it seems likely that there are low-lying hills around it, but it is described as a single dominating peak over the landscape.