When the word molasses was first used in English in the 1500s, it was used in a Scottish dialect to refer to a specific type of alcoholic beverage made from the syrup. During the late nineteenth century, it began showing up in North American newspapers with the modern definition. The term was borrowed from the Portuguese word melaços, which was plural but people just assumed it was singular, which is why we have the plural-sounding ending for an uncountable noun. Melaços comes from Latin mellaceus, meaning "honey-like", with the mel in mellaceus meaning "honey" (and tracing to the Proto-Indo-European reconstruction melit, which also meant "honey"). Historical usage of the word molasses peaked during 1919 and 1941, probably due to the food being used as a substitute for sugar when it was scarce.
Hello! I'm Adam Aleksic, a sophomore studying linguistics and government at Harvard University, where I founded the Harvard Undergraduate Linguistics Society. I also have disturbing interests in politics, vexillology, geography, board games, conlanging, and law.