THERE ARE 295 instances of the word petard in our newspaper database and all but 42 of them have the word hoist (or hoisted) in close proximity. Inspecting a few of those 42 petards that have not been hoisted, however, reveals a horse called Miss Petard, a chipshop owner called Mr Petard, a battleship HMS Petard and a Home Security firm called Petard. A non-hoist petard without a capital P is a rare creature indeed.
A petard was a type of battering ram with an explosive head. To be hoist with one's own petard is to be blown up with one's own weapons: "For 'tis the sport to have the engineer hoist with his own petard" (Hamlet, Act III, scene 4).
The word has a nice etymology: it comes from the same root as the French verb peter, to break wind.