'antivenefic' originates from Neo-Latin/Latin, specifically the word 'antiveneficus', where 'anti-' meant 'against' (from Greek 'antí-') and 'veneficus' related to 'venenum' meaning 'poison'.

'antivenefic' changed from Latin/Neo-Latin 'antiveneficus' (used to describe things acting against poison) and eventually became the modern English adjective and noun 'antivenefic'.

Initially it meant 'acting against or preventing poisoning'; over time it has retained that meaning and also came to be used as a noun meaning 'an antidote'.