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

Researchers found that short dialogues with chatbots designed to engage with believers of antisemitic conspiracy theories led to measurable changes in what people believe. —Staff, FOXNews.com, 28 Nov. 2025

So far, no officials have addressed the conspiracy theories circulating online. —Alia Shoaib, MSNBC Newsweek, 27 Nov. 2025

The last thing anyone needs is our uncle launching into a lengthy complaint about inflation or a sibling presenting her newest conspiracy theory while the stuffing is being passed around. —Dan Rene, Boston Herald, 25 Nov. 2025

On the right, a contingent of MAGA leaders have become vocal adversaries to geoengineering research and are using it to feed conspiracy theories about government manipulation of the atmosphere. —Alexander C. Kaufman, The Atlantic, 24 Nov. 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