A word for a drink acquired a much darker meaning.
Latin potio named a drink. Anglo-French poisun could refer to a drink, potion or poison, and the harmful sense is central to English poison. The selected route shows how an ordinary act of drinking sits behind a much more alarming word.
Middle English lies between the French stage and present-day English; its separate card is omitted.
Source
Merriam-Webster: poisonWord History identifies potio, poisun and their senses; Kids Etymology links the related word potion.