A trebuchet was the classic medieval military siege engine for hurling heavy missiles at an enemy, a big boys’ catapult..
It consisted of a long pivoted arm with a sling at one end and a heavy counterweight at the other. You put a missile in the sling, wound the arm down by windlass and rope and released it by a catch. It was commonly used to pound down the walls of a castle or fortified town during a siege. As an alternative, you might shoot the putrefying corpses of horses over the walls in the hope of infecting the defenders with disease, or perhaps wage psychological warfare by lobbing back your enemies’ severed heads.
Don’t confuse this with a mangonel, a smaller weapon in which the power for flinging the missile came from twisted ropes or animal guts.
The word trebuchet came into English from an Old French word, which at first meant to stumble or trip, a compound of tres, over, with buc, body or trunk. In imitation of later senses of the French word, it has also been used in English for a set of assay scales, an animal trap, and as another name for that instrument of punishment for fraudulent tradespeople, disorderly women and scolds, the ducking-stool or cucking-stool.
You might think the word is as defunct as they get, but there are people around who have re-created them for archaeological research purposes, and others whose hobby is to build and operate the things. One British enthusiast, Hew Kennedy, has used his to hurl grand pianos and old cars about the Shropshire countryside. Asked why, Mr. Kennedy answered, “Well why not? It’s bloody good fun!”.