The eighth power of a number, x⁸, as a single gloriously redundant word. The OED kept it. Of course they kept it.
Robert Recorde needed names for powers before anyone wrote little raised numbers, so he built them by doubling: the zenzic is the square; square that and you have the zenzizenzic, the fourth power; square once more for the zenzizenzizenzic, the eighth. Every “zenzi” is a squaring, and three of them reach x⁸. Notice what that means — you arrive at the eighth power in three multiplications, not seven. The obsolete, ridiculous, six-Z word is a perfect little record of exponentiation by squaring, the trick that still lets a computer raise a number to a thousand-bit power, and so still guards every key you exchange online. Recorde's joke outlived his notation by being, underneath, an algorithm.
In The Whetstone of Witte — the same book that gave the world the equals sign — Robert Recorde faces a problem: there is no notation yet for raising a number to a power. So he names them. Square becomes zenzic, borrowed through Italian and German from the Latin census. The vocabulary is about to get gloriously out of hand.
Recorde's system composes. Zenzic is x². The square of that, x⁴, is zenzizenzic. The square of that, x⁸, is zenzizenzizenzic. Cubes get cubic; mixed powers get names like zenzicube. It is a combinatorial machine for naming exponents, and it produces words with a frankly heroic density of the letter Z.
The whole apparatus existed because superscript exponent notation had not been invented. You could not write x to the eighth; you had to say it. For a few decades, zenzizenzizenzic was not a joke but a working technical term, the honest best that mathematics could do for the eighth power.
When Descartes popularizes the superscript exponent in La Géométrie, x⁸ becomes two characters anyone can write, and the entire zenzi-vocabulary is obsolete almost overnight. A better notation does to these words what better notation always does: it makes them beautiful, useless fossils.
Long dead as mathematics, the word survives in the Oxford English Dictionary, where it holds an unofficial crown: the English word with the most Zs. Lexicographers, bless them, recorded the thing and never let it go. Some words are kept for use; this one is kept for wonder.
Most Zs in English. Longest absurd word. The mathematical term nobody needs and everybody delights in. Zenzizenzizenzic passes from forgotten notation to beloved curiosity, the kind of word that gets screenshotted, shared, and discovered fresh by someone new every single day.
No one will ever again call x⁸ by this name to do arithmetic. And yet the word is more alive than half the working vocabulary of its century, because it is a joy to say and a joy to learn. The eighth power of a number, in one ridiculous, immortal word. The OED was right to keep it.