This is puzzle #3, Quantum of Solitude, from the 2016 MIT Aquarium hunt. I've managed to solve the meta puzzle without finishing this particular puzzle. I haven't found any solutions for this hunt online, but there is an answer-checker on the website.
This is what I tried:
First, I noticed how each category had a word that stood out: The words in the first column are all synonyms of 'calmness' except commotion. The second column is 'the humanities', except chemistry. The third column is 'rivers', except Caribbean. The fourth is 'compound words', except compound. The last column is 'flightless birds', except chickadee. Then, I noticed that all these exceptions have something in common, except two, and that's having double letters. The two exceptions are 'chemistry' and 'compound'. In addition, the references to Dr. Seuss (J. J. HORTON, Seuss Dr., and Solla Sollew) led me to a chemical compound that Dr. Seuss made: oobleck (which I thought was the correct answer because it also had a double letter). However, it seems that my answer is not correct, after checking it with the simulator.
I know from the meta puzzle that it should be a word that fills the blank in
Is it a _______ word?