Petard (pe-TAHRD) Noun: -A small bomb used to blast down a gate or wall. -A loud firecracker. From French péter (to break wind), from Latin peditum (a breaking wind), from pedere (to break wind). Ultimately from the Indo-European root pezd (to break wind) which also gave us feisty, fart, and French pet (fart). Earliest documented use: 1566. So, Petard is a Fart Bomb... apparently. Used in a sentence: "Percy was hoisted by his own petard when he mistakenly took a physagogue instead of a carminative before the big date with Alice.”
The idiom "to hoist by one's own petard" means to have one's plans or scheme backfire.