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

Shortly after the injury was announced Friday, no less than three dozen conspiracy theories popped to explain this odd absence. —Fort Worth Star-Telegram, 20 Oct. 2025

Amanda dismissed conspiracy theories that allege Giuffre did not take her own life. —James Powel, USA Today, 19 Oct. 2025

The dislocation, the way conspiracy theories were passed around like notes in school, the jittery feeling of wanting to grab life with both hands and never let go, has never faded from my memory. —Kate Belli, PEOPLE, 18 Oct. 2025

David Cram’s story is difficult, because there are a lot of conspiracy theories out there about his complicity in Gacy’s life. —Emily Longeretta, Variety, 17 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