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

Considering this is the third time in four years that the logo has predicted who will appear in the big game, fans are convinced that the Super Bowl logo conspiracy theory might have some truth behind it. —Skyler Caruso, People.com, 5 Feb. 2025

Sensible statements, like expressing concern that additives pose potential health dangers, commingle with conspiracy theories. —Brooke Redmond, San Diego Union-Tribune, 2 Feb. 2025

Kennedy is best known as an anti-vaccine activist who spreads conspiracy theories. —Nicholas Florko, The Atlantic, 1 Feb. 2025

After Hurricane Helene ravaged North Carolina, Trump spread baseless conspiracy theories about the Biden administration purposely refusing to help mostly Republican areas and wasting emergency resources on migrants. —Zachary Basu, Axios, 31 Jan. 2025

Word History

First Known Use

1863, in the meaning defined above

Kids Definition

conspiracy theory

noun

: a theory that explains an event or situation as being the result of a secret plot

conspiracy theorist noun