My recent reading has taught me a number of things about the English language I hadn't known before. Here are some of them:
Humble pie: Umbles was the term used for the innards of a deer. This was the worst part of the deer, so naturally it was what the servants ate after the rich folks were served the best parts. When we say we had to eat humble pie, it is a reference to the umbles meat pies once eaten by the lower classes in England. I learned this from The Etymologicon by Mark Forsyth.
Cemetery: From John Ortberg's Who Is This Man? I learned the English word cemetery comes from a Greek word for a dormitory where people would sleep. Early Christians, with their belief in resurrection, adopted the word for burial grounds.
Victorian slang: The letters of Arthur Conan Doyle (A Life in Letters) contain much of interest (I'll have more to say about this book later), but I particularly enjoyed some of the slang terms that were popular 100 years ago and more. Among those Doyle used in his letters are "Reginald has plenty of spondulick" (money); "cheerful as sandboys" (a carefree state of happiness), "I am beginning to get the fidgets" (anxious); "I count those three as two bulls and an outer" (two good stories and one not so good).