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

There is no context here, just names, rattled off by the subject of the 21st century’s most durable conspiracy theory just 41 days before his mysterious death in a jail cell. —Charlie Warzel, The Atlantic, 14 Nov. 2025

Lawsuits, conspiracy theories and protests broke out. —David Smiley, Miami Herald, 10 Nov. 2025

Before the regular season started, the availability of Los Angeles Rams quarterback Matthew Stafford was shrouded in so much secrecy that, at one point, there was a running conspiracy theory that he had been cloned. —Rohan Nadkarni, NBC news, 10 Nov. 2025

Not all conspiracy theories from Republicans were directed at New Jersey Democrats, however. —Brady Knox, The Washington Examiner, 7 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