'balistarius' originates from Latin, specifically the word 'ballista', where 'ballista' meant 'a throwing engine (ballista)' and the suffix '-arius' indicated association or occupation.

'balistarii' changed from Medieval/Latin use: Late Latin/Medieval Latin 'balistarius' (singular) — from Greek 'ballistēs'/'balliste' (related to 'ballein', 'to throw') — and the plural 'balistarii' was used in scholarly and antiquarian English texts to refer to crews of ballista operators.

Initially, it meant 'one who operates a ballista' in Latin and medieval contexts; over time the term has been retained in historical writing with essentially the same meaning, now used mainly as a learned or antiquarian plural form.