'arsenick' originates from Late Latin, specifically the word 'arsenicum', which in turn comes from Greek 'arsenikon' (meaning the mineral orpiment, a yellow arsenic sulfide).

'arsenick' changed from Greek 'arsenikon' into Latin 'arsenicum', then entered Middle English as forms like 'arsenik'/'arsenick' and developed into the modern English noun 'arsenic' and the verb 'arsenick' (to poison with arsenic).

Initially, it referred to the substance (the mineral orpiment/arsenic); over time the word also came to be used as a verb meaning 'to poison with arsenic' and as an adjective describing something affected by that poisoning.