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

Because of the ongoing conspiracy theory about helping the Chiefs, the NFL needs to come out and say what happened Sunday night. —Pete Grathoff, Kansas City Star, 17 Oct. 2025

But as far as conspiracy theories, there was nothing to hang your hat on. —Sean McIndoe, New York Times, 17 Oct. 2025

Our staff deserves better, and this council deserves to be able to do its work without being dragged through endless theatrics and conspiracy theories. —Hema Sivanandam, Mercury News, 16 Oct. 2025

The plans, along with comments by top GOP lawmakers, show how rumors and conspiracy theories can gain an air of legitimacy due to social media and a political climate infused with falsehoods, some political scientists and researchers say. —Stephanie Armour, CNN Money, 16 Oct. 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