Two similar words appeared in The Etymologies of the 1930s: ᴹQ. aryon “heir” as a derivative of the root ᴹ√GAR, and ᴹQ. haryon “(heir) prince” as a derivative of the root ᴹ√ƷAR, both roots having to do with possession (Ety/GAR; Ety/ƷAR). Drafts of these entries had aryo, aryon “son of property = heir” and aryon “heir, prince” (EtyAC/GAR; EtyAC/ƷAR). Based on the gloss “son of property”, I think it is likely the second element of these words is the root ᴹ√YO(N) “son”.
Neo-Quenya: It is possible Tolkien intended haryon and aryon to coexist, but since we have other “prince” words I would just use aryon “heir = one who inherits wealth” for purposes of Neo-Quenya.
A word appearing in the Declension of Nouns (DN) of the early 1930s glossed “grass-stem, reed” and derived from the root ᴹ√RĪI̯ as an example of a monosyllabic vocalic noun (PE21/38). In drafts of this section it was glossed only “reed” (PE21/41 note #147).