Etymology: Middle English arblast, from Anglo-French arblaste, arcbaleste, from Late Latin arcuballista, from Latin arcus bow + ballista — more at arrow
1) A crossbow with a steel box stave. (Wise, Terence. Medieval Warfare, 246)
The arbalest was similar to the crossbow, but it was much larger and more powerful than the crossbow. It also had a greater range.
*term definitions retrieved from Netserf’s Medieval Glossary (http://www.netserf.org/Glossary)