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

During the course of Lindsay’s trial, both Patrick and Danis became subjects of unfounded conspiracy theories. — Nicki Brown, CNN Money, 18 Sep. 2026

According to evidence summarized by the Supreme Judicial Court, Sanders had become consumed by conspiracy theories involving the Illuminati and expressed fears about voodoo before the killings. — Greg Wehner, FOXNews.com, 18 Sep. 2026

Patrick Clancy was also the target of widespread social media conspiracy theories alleging that he was somehow involved in the deaths of his children. — Kristina Rex, CBS News, 17 Sep. 2026

His return to the Senate follows immense speculation, and conspiracy theories, about his health. — David Sivak, The Washington Examiner, 14 Sep. 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