§ Eredhithui, Hithdilias ’Misty Mountains’ (TI:124)
These are earlier names of Hithaeglir, the ’Misty Mountains’.
The first form obviously contains N. ered, pl. of orod ’mountain’ (ÓROT-) and hithui *’misty’ (root KHITH- + adjectival ending -ui), not appearing under KHIS-, KHITH- ’mist, fog’ in The Etymologies, but it appears as the Sindarin name of the month ’November’ (Q. Hísimë) in LotR App. D.
The second word has N. hith ’mist, fog’ and lenited #tilias, apparently a formation from TIL- ’point, horn’, whence N. tild, till ’horn, referring to mountain-peaks’; also S. till ’tine, spike, point’ (PE17:36) The usage of the ending -as (here with i-reduplication from the stem) may be compared with N. pân ’plank, fixed board, especially in a floor’ in comparison with panas ’floor’ (PAN-), thus #tilias – ’mountains’ from a single ’peak, horn’.
If this word had been formed directly from tild, till, one would have expected *tildias, *tillias, however; so one should assume that it comes directly from the root, or by analogy from *til.