The term is defined as someone with a "confident, independent and hedonistic attitude" and has been inspired by Charli XCX's album of the same name that was released in June.
The 'brat summer' became a cultural movement and the word was even adopted by US presidential candidate Kamala Harris in a bid to attract young voters at the start of her election campaign.
Collins' lexicographers analyse social media and other sources to establish which terms should be added to their yearly list of new and notable words.
BREAKING NEWS The Collins Word of the Year is… brat.— Collins Dictionary (@CollinsDict) Find out more about #CollinsWOTY 2024 and see the full list here: https://t.co/gmsnCqA0yv#wordoftheyear #CollinsDictionary #brat #CollinsWOTY pic.twitter.com/Y93NCjFVnoNovember 1, 2024
Other words to feature on the 2024 list include era - inspired by Taylor Swift's tour - and delulu, a diminutive of the word delusional that is defined as being completely mistaken or unrealistic in terms of ideas and expectations.
Alex Beecroft, managing director at Collins, said: "with many of this year's notable words being popularised by generations Z and Alpha, we can confidently say this is the most 'brat' Word of the Year list ever."
The 'Speed Drive' hitmaker - whose real name is Charlotte Emma Aitchison - had enjoyed modest success in the music industry for almost a decade with tracks such as 'Claws' by the time she hit the big time with her chart-topping record 'Crash' in 2022.
Its follow-up - which was released in June - spawned the infamous term that has now ended up in the dictionary, and Charli, 32, previously explained that, to her, the term means a girl who is "volatile" and "honest" with herself.
Speaking in a video posed to TikTok, she explained: "You're just like that girl who is a little messy and likes to party and maybe says some dumb things sometimes."
"Who feels like herself but maybe also has a breakdown. But kind of like parties through it, is very honest, very blunt.
"A little bit volatile. Like, does dumb things. But it's brat. You're brat. That's brat."