English is an omnivorous language and has borrowed heavily from the many languages it has come into contact with, from Celtic and Old Norse in the Middle Ages to the dozens of world languages in the truly global 20th and 21st centuries. You'll be surprised to learn that the impulse to conserve "pure English" is nothing new. In fact, if English purists during the Renaissance had their way, we would now be using Old English compounds such as "flesh-strings" for "muscles" and "bone-lock" for "joint." You may not come away using terms like "whatevs" or "multislacking" in casual conversation, but you'll love studying the linguistic system that gives us such irreverent - and fun - slang, from "boy toy" to "cankles."