Sindarin name of the Misty Mountains, more literally “Line of Misty Peaks” (RC/11), a combination of hîth “mist” (SA/hîth) and aeglir “range of mountain peaks”.
Conceptual Development: In Lord of the Rings drafts from the 1940s, this name first appeared as N. Eredhithui, with Hithdilias written above it (TI/124). In drafts maps from the 1940s Tolkien sometimes wrote Hithaiglin, and that was form of the word in the map in the 1st and 2nd edition of The Lord of the Rings (TMME/379, 383). Tolkien also wrote Hithaeglin in a 1954 letter to Naomi Mitchison (Let/180). However, according to Christopher Tolkien the inclusion of this form of the name in the published version of The Lord of the Rings was an error (SI/Hithaeglir), and it was corrected to Hithaeglir in later editions starting in the 1980s.
Misty mountains; hîth (“mist, fog”) + aeg (S aegas “mountain peak”) + lîr (“range, row”)