bal·lis·ta 
(bə-lĭstə)
(bə-lĭstə)n. pl. bal·lis·tae (-tē′)
An ancient and medieval engine of warfare, usually having a design similar to a crossbow, used to hurl heavy projectiles.
[Latin, from Greek ballistēs, from ballein, to throw; see gwelə- in the Appendix of Indo-European roots.]