ballista

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An ancient and medieval engine of warfare used to hurl heavy projectiles at a target.

Century Dictionary and Cyclopedia

1. n. An ancient military engine used for throwing missiles. The different references to it are contradictory, as it is described as acting by means of a bow, but also as throwing large stones rather than darts. An attempt has been made to reconcile these statements by representing the engine as composed of a strong shaft, rotating on one of its ends, and having at the other end a receptacle for the missile; this shaft would be thrown forward by the recoil of a steel bow, and stopped suddenly against a transom, thus releasing the missile. Throughout the middle ages the term is used in Latin writings for military engines of different kinds. See trébuchet, mangonel, caable, petronel, pierrière, and catapult. When used as a bearing in heraldry, the ballista is represented so simplified as to be hardly recognizable. It has generally two upright posts with a movable bar between them, shown loaded at one end.
2. n. [NL.] In anatomy, the astragalus, a bone of the tarsus.

Wiktionary

1. n. An ancient military engine, in the form of crossbow, used for hurling large missiles.

GNU Webster's 1913

1. n. An ancient military engine, in the form of crossbow, used for hurling large missiles.

WordNet 3.0

1. n. an engine that provided medieval artillery used during sieges; a heavy war engine for hurling large stones and other missiles