Balista, balistæ, fœ. gen. Liu.A croffebowe: a brake or great engine, wherewith a stone or arrow is shot. It may be vsed for a gunne.Balistarium.Plaut.The place where a great brake or sling is layde.
Lewis and Short: Latin dictionary
arcŭ-ballista (better than balista), ae, f. [arcus], a ballista furnished with a bow; only Veg. Mil. 2, 15; 4, 22.