A word for “bone” appearing in the Markirya poem from the 1960s in its plural form axor (MC/222-223). It might be related (conceptually if not etymologically) to the root √AKAS “neck, ridge” (PE17/92).
Conceptual Development: A similar word ᴱQ. as (ass-) bone dates all the way back to the Qenya Lexicon of the 1910s (QL/33). The locative plural of this noun assari “of bones” appeared in the Oilima Markirya poem written around 1930. The form ᴹQ. astŭ- “bone” appeared in the Declension of Nouns from the early 1930s (PE21/27).
Neo-Quenya: While this word could be derived from ✱aksō, I prefer to assume it is derived from ✱ᴺ✶askō with metathesis sk > ks in Quenya. This makes it more etymologically distinct from axë “neck” and also allows a (Neo) Sindarin form ᴺS. asg “bone”, since a Sindarin derivative of ✱aksō would collide with S. ach “neck”.
axo noun "bone"; pl. axor in Markirya