One word was used to epitomize the entire 20th century: #jazz, "to describe not only music, but the sweep and swing of the quintessential American century, and the cultural flows that invigorated it." Ok, it's not the word of the year for 2019, it's the word for the whole 20th C. (Did I mention math, clocks, calendars, counting, and all that jazz, to be my weak spots?)

Who gets to decide such weighty, wordy things? The little-known American Dialect Society (ADS), founded in 1889, and dedicated to the study of the English language in North America.
ADS has been picking a word of the year since 1990, longer than any other entity. Its members selected jazz from dozens of possible words in January 2000. source:
App. Fake news. Hashtag. What will be the word of the decade? And who decides?

Now to see what Gatto said about jazz:

(Just when I thought I was done googling for a minute!)
Over in China, the revered Shanghai Conservatory of Music can’t even believe the principles of jazz are real! That with enough courage and trust in yourself, you can hear a piece of music once, and ring dazzling changes on it forever and ever. They can’t duplicate our jazz. But everything else we make doesn’t worry them a bit.
....The road to wealth comes from understanding yourself. Doing what you do best, not what other people do best.
--John Taylor Gatto,
author of Dumbing Us Down, The Exhausted School, A Different Kind of Teacher, and The Underground History of American Education. Formerly a three-time New York City Teacher of the Year and New York State Teacher of the Year, he “dropped out” of teaching in 1991 via an article in the Wall Street Journal, claiming he was no longer willing to hurt children. He has been writing and talking about non-schooling ever since. https://www.life.ca/lifelearning/0510/breaking_from_the_herd_whats_wrong_with_college_by_John_Taylor_Gatto.htm