If you had asked me just a couple of days back what word in English has the most zs in it, then I would have instantly replied 'pizzazz'. It's the obvious answer (and has a lot of pizzazz).
But I have learned better. The correct answer is 'zenzizenzizenzic', referring to numbers which are "squares of squares squared".
So (if I have it right) 3 squared is 3 x 3 = 9; square that is 81; square 81 and we get 6561. There you go. 6561 is a zenzizenzizenzic number.
The word erupted briefly in the 16c, like a sort of linguistic supernova, but sadly soon faded in favor of 8, more compact but less zedful.