Early Quenya
natto
noun. thing, affair
nat
noun. thing
neta
noun. thing
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. 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”.