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

Despite conspiracy theories, scientists say 3I/ATLAS shows all the signs of being a comet from outside our solar system. —Eric Lagatta, USA Today, 4 Mar. 2026

Proceedings from the nominally closed committee were halted when a Republican leaked an image of Clinton to a conservative influencer, and House Republicans reportedly asked her about UFOs and the Pizzagate conspiracy theory. —semafor.com, 3 Mar. 2026

America’s kitschy Stonehenge — six, 19-foot tall slabs of granite in a cow pasture in Elbert County once thought to be harmless, but transformed into a magnet for conspiracy theories and political extremism. —Eric Mandel, AJC.com, 3 Mar. 2026

Yet Fishback promotes conspiracy theories and trolling language against Jewish people. —Sun Sentinel Editorial Board, Sun Sentinel, 3 Mar. 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