big lie

A big lie is a falsehood so extreme that people believe it precisely because they can't imagine anyone would fabricate something so outrageous.

The term is associated with Nazi propaganda—the idea that massive lies are more credible than small ones because ordinary people tell small lies but wouldn't dare invent colossal ones.

In contemporary use, big lie often describes political disinformation repeated relentlessly until it takes hold: The big lie about the stolen election persisted despite all evidence.