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

Conjecture over that evidence has fueled unsubstantiated conspiracy theories that there might have been a second shooter or that Kirk’s death was staged. — Hannah Schoenbaum, Chicago Tribune, 11 July 2026

Across the country, agitators on the left and the right are increasingly flirting with antisemitic tropes, conspiracy theories and in-jokes to bring in new followers. — Will Carless, USA Today, 10 July 2026

In this way, partial information blackouts can generate more and more distrust in American institutions, creating a vacuum where conspiracy theories can thrive. — Will Gottsegen, The Atlantic, 9 July 2026

But in today’s United States, an aspiring tech dystopia where the news can be weirder than the conspiracy theories? — Judy Berman, Time, 8 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