Polarization started out describing light and ended up describing a country.

Merriam-Webster named it Word of the Year on 9 December 2024, weeks after a bitterly divisive US presidential election. The dictionary defined it as "division into two sharply distinct opposites; especially, a state in which the opinions, beliefs, or interests of a group or society no longer range along a continuum but become concentrated at opposing extremes." It said search volume through the year reflected Americans' wish to understand the complex state of affairs at home and abroad. It also noted how often the word was used across the media, on networks from MSNBC to Fox News, about politics and the election.

Merriam-Webster's editor at large, Peter Sokolowski, stressed that it is a particular kind of division. Polarization, he said, means "tending toward the extremes rather than toward the center." In other words, people can disagree all the time without being polarised; the word applies when the middle ground empties out. He also described the dictionary's role in such a year as a neutral and objective arbiter of meaning for everybody.

It is, in his phrase, a "pretty young word". Polarize came from French optics, where the physicist Étienne-Louis Malus coined it to describe light. Polarization is recorded in English from 1812. It was used figuratively by 1871 and of social and political groups by 1945. The physics sense is still in daily use: polarised sunglasses cut glare by filtering light.

Merriam-Webster's other notable words of 2024 show the same mix of news and pop culture: demure, totality (the eclipse), fortnight (a Taylor Swift song title), allision (the Baltimore bridge collapse), democracy and pander.