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

This sent Teddy down a rabbit hole of Internet conspiracy theories that ultimately led to him latching onto the idea that Michelle is an alien-in-disguise from the Andromeda galaxy who was sent to Earth as part of a plot to wipe out humanity. —Megan McCluskey, Time, 31 Oct. 2025

But in the decades since, the iconic mission has become the source of several major conspiracy theories, primarily one claiming that the landing itself was a hoax entirely staged by NASA. —Eric Lagatta, USA Today, 31 Oct. 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. —Eva Roytburg, Fortune, 31 Oct. 2025

Bugonia is surprisingly subdued for a movie about alien conspiracy theories. —Shirley Li, The Atlantic, 31 Oct. 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