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

Kennedy, who has no background in science, medicine, or public health, is well known as an ardent anti-vaccine activist and peddler of conspiracy theories. —Beth Mole, ArsTechnica, 23 Apr. 2026

He's found success as a media personality by posting news and conservative political commentary, which has espoused various conspiracy theories. —Taijuan Moorman, USA Today, 23 Apr. 2026

For conspiracy theory experts, the missing-scientists saga similarly falls apart on any closer inspection. —Dan Adler, Vanity Fair, 22 Apr. 2026

Jones had repeatedly lied and posited baseless conspiracy theories about the Sandy Hook massacre. —Todd Spangler, Variety, 20 Apr. 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