A noun appearing as G. nast in the Gnomish Lexicon of the 1910s glossed “1) being, abstract; 2) being, creature” (GL/59), a noun form of G. na- “is” (GL/58) based the early root ᴱ√NĀ “be, exist” (QL/64).

Neo-Sindarin: Since √NĀ “be” survived in Tolkien’s later writings, I would retain the noun ᴺS. nast “being”, used for both “a creature” and “the state of existence”.