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

Have people been coming up with conspiracy theories about the play? —Juan A. Ramírez, Vogue, 9 Jan. 2026

The case has drawn intense scrutiny in part because the pipe bomb investigation remained unsolved for nearly five years, fueling speculation and conspiracy theories. —Kaelan Deese, The Washington Examiner, 9 Jan. 2026

The pair become isolated in a rundown Oklahoma motel room as discussions of conspiracy theories take place. —Angel Saunders, PEOPLE, 8 Jan. 2026

A week after what seemed to be the eighth and last episode of the Netflix show’s final season, a conspiracy theory emerged that there would be one more episode—Episode 9—released on January 7, 2026. —Jason Pham, StyleCaster, 7 Jan. 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