conspiracy theory

noun

plural conspiracy theories
: a theory that explains an event or set of circumstances as the result of a secret plot by usually powerful conspirators
the conspiracy theories surrounding Kennedy's assassination
also : a theory asserting that a secret of great importance is being kept from the public
… is best known for … his conspiracy theory that a secret cabal of reptilian humanoids is running the world. Simon Little
… has often been criticized for promoting conspiracy theories such as "birtherism," the theory that President Obama was not born in the U.S. Grace Segers

Examples of conspiracy theory in a Sentence

Conspiracy theories sprung up soon after the leader's assassination.
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
That’s a nearly identical sum to the amount Fox agreed to pay to Dominion Voting Systems in a 2023 settlement over the channel’s airing of conspiracy theories around Dominion’s voting machines, that fueled the fallacy that Trump won the 2020 presidential election. Ethan Baron, Mercury News, 27 June 2025 But as the stakes of the games rise in the 12-team CFP era, the conspiracy theories only get louder. Chris Vannini, New York Times, 18 June 2025 Police said the writings were antisemitic and alluded to a conspiracy theory surrounding the 9/11 attacks. Justin Muszynski, Hartford Courant, 17 June 2025 But those statements stood in stark contrast to the narrative and conspiracy theories that quickly spread online. Elizabeth Robinson, NBC news, 17 June 2025 See All Example Sentences for conspiracy theory

Word History

First Known Use

1863, in the meaning defined above

Time Traveler
The first known use of conspiracy theory was in 1863

Browse Nearby Words

Cite this Entry

“Conspiracy theory.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/conspiracy%20theory. Accessed 8 Jul. 2025.

Kids Definition

conspiracy theory

noun
: a theory that explains an event or situation as being the result of a secret plot
conspiracy theorist noun
Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!