A 2013 SMBC comic that I just saw suggested that the superlative of Fourier is Fouriest. Which reminded me that in 1998, I found a typo in the dictionary.
Here’s the email that I sent to Merriam-Webster about it:
Hi. I was just leafing through my copy of Webster's Ninth New Collegiate, and I found a typo in a guide word. I realize that this dictionary is now ten years old, so it seems quite likely that someone has pointed this out already and it's been corrected (and maybe the item in question isn't even a guide word in the next edition), but I thought it was worth mentioning just in case.
The guide word is on p. 487 and is given as "Fourieriest"; I thought it sounded like a wonderful word (the superlative form of "Fourierier" and "Fouriery," no doubt), but on perusal of the actual entry at the bottom of the page I found that it was, alas, simply "Fourierist," sans the second 'e'.
They politely responded to let me know that it was indeed not a guide word in the 10th edition. Sadly, at some point I think I gave away my copy of the 9th edition, and I neglected to take a photo of the typo.