'arsenicize' originates from English, specifically formed from the noun 'arsenic' and the verb-forming suffix '-ize' (from Greek '-izein' via Latin/French), where 'arsenic' came from earlier Latin/Greek names for the element and '-ize' meant 'to make or render'.

'arsenic' changed from Greek word 'arsenikon' to Latin 'arsenicum' and into Middle English as 'arsenic'; the modern English verb 'arsenicize' was created by adding the productive suffix '-ize' to the noun 'arsenic'.

Initially, the root referred to the chemical element 'arsenic'; over time the derived verb came to mean 'to make or treat with arsenic', which is the current usage.