To debunk something (such as a belief or theory) is to show that it is not true.

// The influencer remained enormously popular despite having the bulk of their health claims thoroughly debunked.

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“Conspiracy theorists (and those of us who argue with them have the scars to show for it) often maintain that the ones debunking the conspiracies are allied with the conspirators.” — Adam Gopnik, The New Yorker, 24 Mar. 2025

To debunk something is to take the bunk out of it—that bunk being nonsense. (Bunk is short for the synonymous bunkum, which has political origins.) Debunk has been in use since at least the 1920s, and it contrasts with synonyms like disprove and rebut by suggesting that something is not merely untrue but is also a sham—a trick meant to deceive. One can simply disprove a myth, but if it is debunked, the implication is that the myth was a grossly exaggerated or foolish claim.