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

The president’s gusher of disinformation and conspiracy theories is designed to create support for voter suppression measures, including passing the SAVE America Act, which could keep millions from casting ballots. — Sun Sentinel Editorial Board, Sun Sentinel, 18 July 2026

Antisemitic rhetoric promoting stereotypes and conspiracy theories against Jews is going viral online. — Will Carless, USA Today, 17 July 2026

Officials said the suspects harbored fringe conspiracy theories and hoped the attack would destabilize the government. — Julie Carr Smyth, Los Angeles Times, 16 July 2026

At the same time, Mitch McConnell’s prolonged absence from the Senate is inspiring conspiracy theories as well. — David A. Graham, The Atlantic, 15 July 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