Early Quenya
natto
noun. thing, affair
nat
noun. thing
neta
noun. thing
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A word appearing as ᴱQ. natto “thing, affair” in the Qenya Lexicon of the 1910s, an elaboration of ᴱQ. nat “thing” under the early root ᴱ√NĀ “be, exist” (QL/64). The word reappeared with the glosses “affair, matter, thing” in the English-Qenya Dictionary of the 1920s with a plural nattur indicating a stem form of nattu-, but this entry was deleted (PE15/68).
Neo-Quenya: I’d retain ᴺQ. natto (nattu-) for purposes of Neo-Quenya since both Q. nat “thing” and √NĀ survive in Tolkien’s latter writings, but I would limit its sense to “affair, matter” as in “✱a thing that is happening/has happened”.