A word appearing as ᴱN. asg “bone” in Early Noldorin Word-lists of the 1920s (PE13/137, 160). G. asg “bone” also appeared in the Gnomish Lexicon of the 1910s with a variant form asc and the glosses “bone (especially of other animals, rarely of men); stone of fruit” (GL/20). This 1910s form was clearly related to ᴱQ. as “bone” from the contemporaneous Qenya Lexicon (QL/33).
Neo-Sindarin: In the 1960s, Tolkien used the Quenya word axo for bone (MC/223) and Fiona Jallings suggested ᴺS. ach as its Sindarin equivalent. Unfortunately, that clashes with attested S. ach “neck” (PE17/92), so I prefer to retain ᴺS. asg for “bone”, and assume it is derived from primitive ✱ᴺ✶askō, where the primitive sk became sg in Sindarin, just as it did in earlier iterations of the language.
In the Gnomish Lexicon of the 1910s, Tolkien had G. acha “waterfall” as a cognate to ᴱQ. aksa (GL/17). Its form became âch in Gnomish Lexicon Slips adding to that document (PE13/108) and ach in Early Noldorin Word-lists from the 1920s (PE13/136, 158).