a device contrived to hurt another person; boobytrap; an explosive contraption used in warfare to blow in a door or form a breach in a wall.
to "hoist by one's own petard" means you have been hurt or caught by the very device that you intended to hurt someone else. This phrase is often used mockingly, as if to say that you stepped in your own mess.
A nasty and insulting word for members of PETA, an animal-rights terrorist organization. They are usually destroying property or protesting at McDonalds.
An idiot PETArd threw paint on my fur coat, so I sued her for over a million dollars and won.
Medieval demolition. Set down by people, and then the person runs. In many cases, the person mayfail to run, therefore they have been "blown away by their own petard", which is also a common saying.