A catapult is any kind of device that shoots or launches a projectile by mechanical means. In England, a catapult is what we call a slingshot in the US. A catapult is also the part of an aircraft carrier that launches airplanes off the deck.

But for our purposes, a catapult is any of the ancient types of artillery, including Onagers, Scorpions, Trebuchets, Ballistae, Springalds, Coullards, Bricoles Perriers and more.

But most people tend to think of a catapult as the one-armed torsion machine used by the Romans. This is also known as the Onager or Mangonel.

The word Mangonel derives from the ancient Greek word "Manganon", literally meaning "engine of war". The Romans called it a Manganum. In pre-medieval French the word Manganum was changed to Manganeau, and the English changed that to Mangonel in the 1300s.

The history gets a little sketchy in the middle ages, but some historians believe that "mangonel" was shortened to the word "gonnel" about the same time that cannons were being developed, and later still, "gonnel" was shortened to "gun." And still today, in the military a "gun" is strictly a piece of big artillery.

Onager is originally the name for the wild Asian donkey. This donkey bucks like a bronco if anyone gets too close to it, and it is known to kick stones at people and predators too. So when the Romans needed a name for their one-armed torsion catapult, they called it the Onager!

The Onager (catapult) has a single arm that is powered by a large skein of twisted ropes. The ropes were usually made from hair or sinew for their elastic properties.

The word "Trebuchet" is originally French, and meant something like "to fall over or rotate about the middle" as in a see-saw rotating on its axle. It also seems to have meant a big, heavy beam. Today a Trebuchet is any kind of catapult that is powered by a massive counterweight on one end of an arm, and a sling on the other end. This includes Perriers, or "traction" trebuchets which are powered by a mass of people pulling one end of the arm with ropes.

This is a two-armed torsion device invented by the Greeks. It works similar to a crossbow, but instead of a flexible bow, it uses two stiff arms powered by twisted rope skeins like an Onager. The ballista predates the Onager by several centuries and was used to hurl stones (lithobolos style ballista) and also bolts or darts.

Obviously, this is where we get the word "ballistic".