petard

A petard was originally a small explosive device used in siege warfare to blow open gates or walls. Today, the word is best known from the idiom "hoist with one's own petard," made famous by Shakespeare. In modern use, that phrase usually means someone is harmed by their own plan or trapped by the very trick they meant for someone else. If you try to cheat or trap another person and your own plan ends up ruining things for you, that is the idea behind it.

The word "petard" comes from the 16th-century French pétard, a small metal device filled with gunpowder and used to break through gates, doors, or walls. It is related to the French verb péter, meaning "to fart," probably a joking reference to the loud burst it made. Soldiers fixed these charges to fortifications, which was dangerous work because the person placing the device could be injured if it went off too soon.

William Shakespeare made the word famous in Hamlet. In Act 3, Hamlet speaks of turning a plot back on those who planned it and says it is a pleasure to see "the enginer / Hoist with his own petar." In that context, "hoist" means blown upward or blown up. So the image is quite literal: the person who sets the bomb is blasted by his own bomb. From that vivid picture came the modern figurative meaning.

Today, we rarely see real petards outside of history books or museums, but the idiom remains common in educated English. It describes a situation in which a harmful or clever scheme backfires and hurts the person who created it. The phrase often carries a sense of irony or poetic justice, because the planner becomes the victim.

For example: "The politician tried to smear his opponent with a leaked recording, but the full tape revealed his own corruption, leaving him hoisted by his own petard." Or: "She thought she could skip the group project and let others do the work, but the teacher assigned individual grades based on participation, and she was hoisted by her own petard."

Ultimately, the word began as the name of a real explosive device, but it now lives mostly in a phrase about irony: being defeated by your own plan.