Merriam-Webster's Word of the Day for March 10, 2010 is:

petard • \puh-TAHRD\  • noun
1 : a case containing an explosive to break down a door or gate or breach a wall *2 : a firework that explodes with a loud report

Example sentence:
"The blast occurred on Sunday afternoon in a farmer's house in the Anhui Province, destroying six rooms which stored materials for making petards and firecrackers." (RIA Novosti, January 11, 2010)

Did you know?
Aside from historical references to siege warfare, and occasional contemporary references to fireworks, "petard" is almost always encountered in variations of the phrase "hoist with one's own petard," meaning "victimized or hurt by one's own scheme." The phrase comes from Shakespeare's Hamlet: "For 'tis the sport to have the enginer / Hoist with his own petar." "Hoist" in this case is the past participle of the verb "hoise," meaning "to lift or raise," and "petar(d)" refers to an explosive device used in siege warfare. Hamlet uses the example of the engineer (the person who sets the explosive device) being blown into the air by his own device as a metaphor for those who schemed against Hamlet being undone by their own schemes. The phrase has endured, even if its literal meaning has largely been forgotten.

*Indicates the sense illustrated in the example sentence.