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).
An unglossed word appearing as ᴱQ. aksīna in the English-Qenya Dictionary of the 1920s, an adjectival form of ᴱQ. akse “steel” (PE15/77). It appeared after the partitive form aksīnen of the noun, which could also function as an adjective meaning “of steel” as mentioned in the contemporaneous Early Qenya Grammar (PE14/48). It could be that aksína had the same meaning, or a slightly different meaning such as “✱like steel”.
Conceptual Development: In the Qenya Lexicon of the 1910s it was ᴱQ. yaksina “of steel” based on ᴱQ. Y̯akse “steel” (QL/105).
Neo-Quenya: I would retain adjective ᴺQ. axína “(of) steel, ✱like steel” for purposes of Neo-Quenya since I also retain the noun ᴺQ. axë “steel”.