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

This trait has derailed lives when the model encourages someone to believe in their own delusions and conspiracy theories, and in one tragic case has been blamed for a teenager’s suicide. —Eliza Strickland, IEEE Spectrum, 7 Aug. 2025

That assassination, of course, launched a million conspiracy theories: Most Americans still believe that the shooter, Lee Harvey Oswald, did not act alone. —Kaitlyn Tiffany, The Atlantic, 7 Aug. 2025

The conspiracy theories have gotten widespread airplay in recent weeks. —Ron Kampeas, Sun Sentinel, 4 Aug. 2025

But both Kazuya and Watase quickly distanced themselves from the party as Kamiya grew its base largely on the back of promoting conspiracy theories related to the 2020 U.S. election, COVID-19, and more. —Chad De Guzman, Time, 1 Aug. 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