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

Musk and Altman's feud escalates The conflict between Tesla CEO Elon Musk and OpenAI CEO Sam Altman has intensified after Musk amplified a conspiracy theory that an OpenAI whistleblower, whose death had been officially deemed a suicide, was actually murdered. —Diane Brady, Fortune, 12 Sep. 2025

An advocate for free speech and limited government, Kirk also used his sizable platform to spread falsehoods and conspiracy theories about topics including climate change, vaccines, transgender people and demographic change. —Rachel Treisman, NPR, 11 Sep. 2025

While conspiracy theories swirled online about his death, Trump himself even retweeted a conspiracy theory connecting Clinton to Epstein's death. —Martha McHardy Rahman, MSNBC Newsweek, 11 Sep. 2025

Almost as quickly as the condemnations of political violence came the conspiracy theories on the shooting. —Kinsey Crowley, USA Today, 11 Sep. 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