Collins defines "climate strike" as "a form of protest in which people absent themselves from education or work in order to join demonstrations demanding action to counter climate change," CBS News reported.

The dictionary first registered the word in 2015, when it was first used to describe protests coinciding with the UN Climate Change Conference in Paris. But its usage spiked this year with the rise of the global movement inspired by Swedish teenager Greta Thunberg. Collins said its usage increased by 100 times in 2019.

"Climate strikes can often divide opinion, but they have been inescapable this last year and have even driven a former word of the year – Brexit – from the top of the news agenda, if only for a short time," Collins' language content consultant Helen Newstead told The Guardian. Brexit was the word of the year in 2016, according to BBC News.

The word of the year is chosen from a shortlist of 10 new terms that Collins lexicographers notice proliferating in newspapers or online, BBC Newsround explained.

This is the second year in a row that the final pick has reflected environmental concerns. 2018's word of the year was "single-use," referring to often-plastic products that are designed to be used once and then thrown away, where they can end up in the ocean and threaten marine life.

Both "climate strike" and "single-use" have seen a four-fold increase since 2013, as news stories and programs like BBC's Blue Planet II have raised awareness of the multiple crises facing Earth's ecosystems, the dictionary said.

"Climate strike" wasn't the only environmental word on the 2019 shortlist. Another contender was "rewilding," defined as "the practice of returning areas of land to a wild state, including the reintroduction of animal species that are no longer naturally found there."

Some consider rewilding as one solution to the climate crisis, CNN pointed out. One group has argued that returning a quarter of the UK to nature could draw down 47 million tons of carbon dioxide out of the atmosphere each year.

The other words on the 2019 shortlist were bopo, a body positivity movement; cancel, for ceasing to acknowledge someone publicly as a form of censure; deepfake, a false image or video that appears unedited or the act of making one; double down, to increase one's commitment despite opposition; entryist, someone who joins a political party to change it; hopepunk, an artistic and literary movement that promotes positive action despite difficult circumstances; influencer, someone who uses social media to promote brands or lifestyles; and nonbinary, for a gender or sexual identity that refuses the binary categories of male or female, homosexual or heterosexual.