Source : Webster's Revised Unabridged Dictionary (1913)

Trebuchet \Treb"u*chet\, Trebucket \Tre"buck*et\, n. [OF.
   trebuchet, trebukiet, an engine of war for hurling stones, F.
   tr['e]buchet a gin, trap, a kind of balance, fr. OF.
   trebuchier, trebuquier, to stumble, trip, F. tr['e]bucher.]
   1. A cucking stool; a tumbrel. --Cowell.

   2. A military engine used in the Middle Ages for throwing
      stones, etc. It acted by means of a great weight fastened
      to the short arm of a lever, which, being let fall, raised
      the end of the long arm with great velocity, hurling
      stones with much force.

Source : WordNet®

trebucket
     n : medieval artillery used during sieges; a heavy war engine
         for hurling large stones and other missiles [syn: {catapult},
          {arbalest}, {arbalist}, {ballista}, {bricole}, {mangonel},
          {onager}, {trebuchet}]