Hoist with his own petard" is a phrase from a speech in William Shakespeare's play Hamlet that has become proverbial. The phrase's meaning is that a bomb-maker is blown ("hoist", the past tense of "hoise") off the ground by his own bomb ("petard"), and indicates an ironic reversal or poetic justice.[1]

In modern vernacular usage of the idiom, the preposition "with" is commonly exchanged for a different preposition, particularly "by" (i.e. "hoist by his own petard") or "on", the implication being that the bomb has rolled back and the unfortunate bomb-maker has trodden on it by accident. The latter form is recognized by many British and American English dictionaries as an interchangeable alternative.