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

For all its drama — the tearful testimony, the corporate conspiracy theories, the government’s fully victorious verdict — Brian Watson’s civil fraud trial ended quietly last month. —Justin Wingerter, Denver Post, 18 Feb. 2026

Unverified theories and wild speculation are sapping law enforcement resources, flooding tip lines with false leads and spawning conspiracy theories targeting innocent people, including family members. —Hannah Fry, Los Angeles Times, 18 Feb. 2026

The widespread interest in the Guthrie case has spawned endless speculation and conspiracy theories in the press and on social media. —Timothy Nerozzi, The Washington Examiner, 16 Feb. 2026

And conspiracy theories don’t need much to grow. —Joe Rexrode, New York Times, 14 Feb. 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