ᴱN. cas n. “skull” (Category: Skull)
A noun appearing as G. cas “head, skull” in the Gnomish Lexicon of the 1910s, where Tolkien said it was “only used of physical head of bodies” (GL/25). It was clearly derived from the early root ᴱ√KASA “head” (QL/31). The word ᴱN. cas “skull” reappeared in Early Noldorin Word-lists of the 1920s (PE13/140). Given the tendency of non-initial s to vanish in later iterations of the language (something that was not a feature of Gnomish of the 1910s), Tolkien likely abandoned this word; in The Etymologies of the 1930s, ᴹ√KAS “head” had no Noldorin derivatives (Ety/KAS).
Reference ✧ PE13/140 ✧ “skull”