I do enjoy me strolls down etymology lane, I’m not gonna lie. Though I never considered that “to learn” actually meant the same as “to teach” for a fair chunk of English-speaking history. According to Merriam-Webster–whose Word of the Day is totally worth a subscribe–there was a good half century where it was the norm. They write:
From the 13th through the end of the 18th century the use of learn to mean “teach” was fairly common, although the 1785 edition of Samuel Johnson’s dictionary (the 6th edition) labeled it as obsolete. And while Noah Webster used it in his letter writing that year, by the time he published his dictionary in 1828 this sense of the word had either taken a turn for the worse, or someone had teased him about using it thusly, as he seems to have changed his mind about it. Webster did define learn as “to teach, to communicate the knowledge of something before unknown,” but included a note at the end of the entry, “this use of learn is found in respectable writers, but is now deemed inelegant as well as improper.”
Read the whole story over on M-W’s website. They’ll learn you something good.