Early Quenya
akse
noun. steel
yakse
noun. steel
yaisa
noun. steel
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
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).