1. A small bell-shaped bomb used to breach a gate or wall.
2. A loud firecracker.
be hoist with one's own petard
To be undone by one's own schemes.
[French pétard, from Old French, from peter, to break wind, from pet, a breaking of wind, from Latin pēditum, from neuter past participle of pēdere, to break wind; see pezd- in the Appendix of Indo-European roots.]
Word History: The idiom to be hoist by one's own petard originates in Shakespeare's Hamlet (written around 1600). In the play, Claudius, the Danish king and Hamlet's stepfather, entreats two of Hamlet's schoolfellows, Rosencrantz and Guildenstern, to betray Hamlet—the pair are to escort Hamlet to England, carrying a letter instructing the English king to put Hamlet to death. Learning of the plot to kill him, Hamlet contemplates how to turn the tables against them: "For 'tis the sport to have the enginer / Hoist with his own petar; and't shall go hard / But I will delve one yard below their mines / And blow them at the moon." Hoist is the past participle of hoise, an earlier form of the verb hoist, "to be lifted up," while a petar or petard is a small bomb used in early modern warfare. The phrase "hoist with his own petard" therefore means "to be blown up with his own bomb." Contemporary audiences must have been struck by Shakespeare's turn of phrase, because it soon became a commonplace expression in 17th-century English.
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