Another quickie from the OED. When the word “treacle” entered English in the Middle Ages, it meant “antidote against poison, venomous bites and disease”; it came via Old French and Latin from the Greek “theriake” (antidote against venom), from “therion” (wild beast). Treacle seems to have retained this meaning until the beginning of the 19th century, though in the broader sense of “medicine or remedy”. The use of syrup to make medicine taste better led to the current sense, which dates from the late 17th century.