The noun ᴱQ. yaksi “cow” appeared in the Qenya Lexicon of the 1910s as a derivative of the early root ᴱ√Ẏak “a head of cattle” (QL/105). The contemporaneous Gnomish Lexicon also had ᴱQ. yaksi, but this form was deleted and ᴱQ. yakse was given as the cognate of G. gach “milch cow” (GL/36).
Conceptual Development: In Early Qenya Word-lists of the 1920s, the word for “cow” was ᴱQ. mui (PE16/132), likely related to G. mûs “cow” from the Gnomish Lexicon of the 1910s which had a deleted variant {mui} (GL/58). This probable relationship was suggested by Patrick Wynne and Christopher Gilson (PE16/132).
Neo-Quenya: For purposes of Neo-Quenya, I would adapt this word as ᴺQ. yaxë from the Neo-Root ᴺ√GYAK; Helge Fauskanger used this word for “cow” in his NQNT (NQNT).
A word appearing as ᴱQ. akse “steel” in the English-Qenya Dictionary of the 1920s (PE15/77), also appearing in its partitive form aksínen “of steel” in the Early Qenya Grammar of this same period (PE14/48, 81). Based on its partitive form as well as its adjective form ᴱQ. aksína, I believe its stem form would be aksi-.
Conceptual Development: In the Qenya Lexicon of the 1910s it was ᴱQ. Y̯akse “steel” (QL/105), while in the contemporaneous Gnomish Lexicon it was {yakse >>} yaisa “steel” (GL/37).
Neo-Quenya: For purposes of Neo-Quenya I would stick with ᴺQ. axë (axi-) “steel” based on the Neo-Root ᴺ√GAK. This “steel” word does conflict with the later word Q. axë “neck” (PE17/92), but I think a stem form of axi- makes it sufficiently distinct. However, if you are uncomfortable with this, the later word tornanga “hard-iron” might also be used for “steel” (PE17/56).