Old French was the form of the French language spoken and written in northern France from roughly the 9th to the 14th century. If you tried to read a book written in Old French today, you'd recognize some words but find much of it confusing, like when you see Shakespeare's English and have to puzzle out what he meant.

Old French matters because it's the source of thousands of English words. When William the Conqueror invaded England in 1066, he brought Old French with him, and for the next few centuries, Norman French was the language of England's kings, nobles, and courts. This is why English has so many French-origin words, especially for government (justice, parliament), food (beef, pork), and law (attorney, verdict).

Old French gradually evolved into Middle French and eventually modern French. When you see “from Old French” in a dictionary etymology, it means the English word entered our language during those medieval centuries when French and English were mixing together in England. Words like castle, merchant, and royal all traveled from Old French into English, where they've stayed for nearly a thousand years.