Zzxjoanw is a famous lexicographic hoax, perpetuated by Rupert Hughes. Mr. Hughes was an American novelist, film director, screenwriter, military officer, composer, and most importantly for the subject at hand, the author of the The Musical Guide (1903), an encyclopedia of classical music. Included in this was a pronouncing dictionary, and the last entry in this section was as follows:
zzxjoanw (shaw). Maori. 1. Drum. 2. Fife. 3. Conclusion.
People believed this. Zzxjoanw has appeared in numerous 'weird word' collections, and has been frequently cited as an excellent Scrabble word, despite the vanishingly small chances of ever actually being able to play it, and the fact that it does not appear in Scrabble dictionaries. Or regular dictionaries, for that matter.
Another problem with this word is that it is quite unlikely that, if it actually existed, it would be pronounced 'shaw'. One dictionary, Mrs. Byrne's Dictionary of Unusual, Obscure, and Preposterous Words (1974), attempted to fix this by giving the pronunciation as "ziks-jo'an". It is probable that the pronunciation is a jab at (or tip of the hat to) George Bernard Shaw, a proponent of Spelling Reform and the creator of the word ghoti.
Other problems include the fact that Maori does not have the letters 'z', 'x', or 'j'1, and that Maori words end in a vowel. It is also questionable that the Maori language would have a word for fife, and if it did, that it would be the same word as for drum2. It is also quite a coincidence that the last word in the dictionary happens to mean 'conclusion'.
Despite all of this, it wasn't until 73 years later that Philip Cohen published an essay, What's the Good Word? in the November 1976 issue of Word Ways: The Journal of Recreational Linguistics3, in which he enumerated the problems noted above. He is generally credited with uncovering the hoax, although he must surely not have been the first to notice that something odd was going on. Regardless, he was apparently the first one to bother researching the Maori language regarding this point.
However, one mystery remains: I have not been able to determine who Joan was4.
Footnotes:
1. Or the sound 'sh', making the pronunciation key suspect for yet another reason. In fairness, Maori does have a voiceless bilabial fricative (IPA /ΙΈ/), which does not appear in English, and might possibly be transcribed as 'zz'.
2. It is, perhaps, worth noting that the Maori koauau is a small, flute-like pipe that could conceivably be loosely translated as 'fife', if one was not too picky in their definitions.
3. I have not been able to gain direct access to this article myself. If you are interested in tracking it down, look for: Cohen, Philip M. (1976) "What's the Good Word?," Word Ways: Vol. 9: Iss. 4, Article 2.
4. Not as some have suggested, a reference to George Bernard Shaw's Saint Joan, as that was not published until a few decades later.