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

In the two weeks since the Justice Department failed to fully meet a legal deadline to release its expansive tranche of files on Jeffrey Epstein, old conspiracy theories about his life and death have subsided and new ones have taken shape. —Stephen Fowler, NPR, 2 Jan. 2026

But observers found kids arriving at Quality Learning Center that same afternoon, resulting in a raft of online conspiracy theories. —Andy Rose, CNN Money, 1 Jan. 2026

Those who peddle conspiracy theories, defame innocent Americans, and wish death upon their political rivals should leave the state. —Krista Kafer, Denver Post, 31 Dec. 2025

The unlock in my brain for why conspiracy theories are so popular now in, in culture—they’ve always been popular; obviously the paranoid mind is a fixture in all of history, but especially American history. —David Frum, The Atlantic, 31 Dec. 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