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

Recent reports revealed that Collins’ son-in-law’s social media accounts contained white nationalist content, Nazi imagery and conspiracy theories. — Aj Willingham, AJC.com, 31 July 2026

Headlines often focus on young people, especially teen boys and young men, who have been drawn into hateful movements, conspiracy theories or even violence after spending time in online communities. — Larry Magid, Mercury News, 30 July 2026

But conspiracy theories can transform the absence of evidence into evidence of concealment. — Art Jipson, The Conversation, 30 July 2026

No updates about McConnell’s condition were shared for nearly four weeks, prompting speculation and conspiracy theories. — Siladitya Ray, Forbes.com, 29 July 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