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

Epstein's life, crimes and death continue to fuel conspiracy theories, as well as political fallout for those with ties to the disgraced financier. —Rachel Treisman, NPR, 7 May 2026

This suggestion added fuel to a growing MAGA conspiracy theory that the indictment showed the far-right violence in Charlottesville in 2017 to have been a setup somehow planned by the SPLC. —Quinta Jurecic, The Atlantic, 3 May 2026

In the minutes, hours and days following Saturday’s interrupted White House Correspondents’ Association dinner, Americans were inundated by falsehoods and conspiracy theories from nearly every flank. —Jane Lytvynenko, NBC news, 3 May 2026

Kelly told Stahl that conspiracy theories can be a powerful tool for far-right and hate groups to find new audiences. —Will Croxton, CBS News, 3 May 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