The Collaborative International Dictionary
Petrary \Pet"ra*ry\, n. [L. petra stone. Cf. Sp. petraria, and E. Pederero.] An ancient war engine for hurling stones.
Wiktionary
n. A weapon used to hurl stones
Wikipedia
Petrary is a generic term for a medieval stone-throwing siege engine (from the Greek "petra", "stone"), used to hurl large rocks against the walls of the besieged city, in an attempt to break down the wall and create an entry point.
Petraries can be either gravity operated, where a large counterweight drops to propel the missile, or tension operated, where the throwing arm is pulled back against twisted rope or animal sinew, which then provides the power when released.
Catapult, trebuchet, mangonel are all types of petrary, but ballista style armaments, which shot bolts or arrows, would not fit into this category.
Usage examples of "petrary".
Each hull was dominated by a gigantic catapultnot the small petrary that some warships carried, but a massive siege engine of the type that normally was constructed to breach a walled town or fortress.
The petraries had scarcely fired a first volley when the Scylredi craft attacked.