Description

A petard was a small bomb used to blow up gates and walls when breaching fortifications.

The word remains in modern usage in the phrase to be hoisted by one's own petard (or to be hoist with one's own petard), which means "to be harmed by one's own plan to harm someone else" or "to fall into one's own trap", literally implying that one could be lifted up (hoisted, or blown upward) by one's own bomb.