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

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

Word History

First Known Use

1863, in the meaning defined above

Rhymes for conspiracy theory

• beery
• bleary
• cheery
• cirri
• dearie
• deary
• dreary
• eerie
• kiri
• leary
• leery
• peery

Kids Definition

conspiracy theory

noun

: a theory that explains an event or situation as being the result of a secret plot

conspiracy theorist noun