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

Greene, who raised eyebrows in recent years by backing unfounded conspiracy theories, has strayed from the GOP on issues such as healthcare, the record-setting government shutdown, and the Jeffrey Epstein files. —Kimi Robinson, USA Today, 7 Nov. 2025

And some, like Fuentes, are resurfacing centuries-old Christian conspiracy theories about the Jewish people. —Geoff Brumfiel, NPR, 7 Nov. 2025

The crash has drawn a range of reactions — from conspiracy theories that suggest a government plot to sicken people to serious responses from people who oppose experimenting on animals. —Emma Burleigh, Fortune, 4 Nov. 2025

Her family did not share details about her death publicly, but Massie quickly shut down internet conspiracy theories. —Meredith Kile, PEOPLE, 3 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