Saying one thing while meaning another, often the opposite. The true meaning is left to the reader or listener.
In Julius Caesar
Friends, Romans, countrymen, lend me your ears! / I come to bury Caesar, not to praise him.
Antony says he has come "to bury Caesar, not to praise him," but the rest of his speech does exactly that. The phrase promises modesty and means the opposite, and it is already an orator's trick for winning over the crowd.
Act III: The Assassination and the Forum, Mark Antony
But Brutus says he was ambitious, / And Brutus is an honorable man.
Act III: The Assassination and the Forum, Mark Antony
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