late 14c., "warlike munitions," especially ballistic engines, from Anglo-French artillerie, Old French artillerie (14c.), from artillier "to provide with engines of war" (13c.), which probably is from Medieval Latin articulum "art, skill," a diminutive of Latin ars (genitive artis) "art." But some would connect it to Latin articulum "joint," others to Latin apere "to attach, join," and still others to Old French atillier "to equip," altered by influence of arte.
Originally any engine for discharging missiles (catapults, slings, bows, etc.); the modern restriction to "ordnance, large guns" is from 16c. Technically, "all firearms discharged from carriages," as opposed to small arms, discharged by hand. As a branch of the army, from 1786.