Old French invents a verb that can only mean killing

Speakers of Old French inherited a noun, puison, from the Latin word for a drink, and it kept both the senses Latin had carried. A puison could be a medicine and it could kill. Around 1130 they built something new out of it, the verb empoisonner, which meant to kill by poison and carried no other sense. By the end of the thirteenth century they had added a noun for the person who did it. Anglo Norman speakers took the verb across the channel in the fourteenth century, shortened it, and made their own word for the doer. The direction of the change is the evidence. Nobody needed a verb meaning to give medicine. People needed a word for a particular fear, and once the word for the person existed, the person existed as a type. The French colonists who reached the Caribbean four centuries later brought this vocabulary with them and applied it to the enslaved.