I cannot help about etymology, only add that Judeo-Neo-Aramaic also has this word, and also root z-q-n-b in general, usually as (eat) poison, meaning go to hell. As far as I know Kurdish (at least certain dialects) also shares it. Yet these are likely to be borrowed from Iraqi.
Thanks Origumi. The -uut ending made me suspect that the word entered Arabic from Aramaic, and the fact that the word exists in Jewish Neo-Aramaic makes me a little more confident in this.
I'm not sure I'm clear on what is meant by the entry for the z-q-n-b root in general. Does the Aramaic have the verb zaqnab as well as the word zaqnabuut? I think I will look up this book in the library.
Thanks once again.