Early Quenya
tanka
noun. fastening, rivet
tanka
adjective. firm, fixed, fast; steady, (stead)fast
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 noun appearing as ᴱQ. tanka “fastening, rivet” in the Qenya Lexicon of the 1910s written under the adjective ᴱQ. tanka “firm, fixed, fast, steady”, both based on the early root ᴱ√TAKA “fix, fasten” (QL/88).
Neo-Quenya: The root √TAK and adjective tanca survive in Tolkien’s later writing, so I think the noun ᴺQ. tanca “fastening, rivet” can also be retained for purposes of Neo-Quenya, perhaps as a nominalized form of the adjective.