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

Election officials are debunking a years-old conspiracy theory. — Kayla Hayempour, NBC news, 16 Oct. 2026

The Texas Democrat returned to the campaign trail last weekend after more than a week away with the flu, as conspiracy theories from right-wing activists spread like wildfire across social media. — Lauren Green, The Washington Examiner, 15 Oct. 2026

The conclusion and the conspiracy theory is my phone is listening to my conversations. — Nilay Patel, The Verge, 15 Oct. 2026

With these conspiracy theories swirling, some researchers are now seeing the models more as competitors than tools—and the use of them as a betrayal. — Peter Hall, Scientific American, 13 Oct. 2026

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