A root in The Etymologies of the 1930s glossed “sharp, pointed”, with derivatives like ᴹQ. aika/N. oeg “sharp” and ᴹQ. aiqa “steep” (Ety/AYAK). Similar forms appear in the Qenya Lexicon of the 1910s such as ᴱQ. aiqa “steep” and ᴱQ. aiko “cliff”, though Tolkien did not produce an explicit early root for these words, marking it instead as “?” (QL/29). The early root might have been ✱ᴱ√AIK(W)-. Early Noldorin forms from the 1920s such as ᴱN. aig “high, steep” and ᴱN. aiglir “peak, mountain top” indicate the root was also adopted in the other branches of the Elvish languages (PE13/158).
The evolution ᴱN. aiglir >> N. oeglir >> S. aeglir “mountain peaks” indicate this root’s continued validity in Tolkien’s later conception of the language, as seen in S. Hithaeglir “Misty Mountains” (Let/180; RC/11; S/54). The element S. aeg “sharp” (<< N. oeg) appears in a variety of other late names such as S. Aeglos “Snow-point” (S/294) and S. Aegnor “Sharp Flame” (MR/323). Tolkien gave an alternate etymology for the last name as a phonetic adaptation of Q. Aicanáro “Fell Fire” (PM/346-347), but that variant was based on a different root √GAYA “awe” > ✶gayakā “fell, terrible” (PM/363), so it did not necessarily invalidate √AYAK “sharp, pointed”.