“According to the lovely folks at Merriam-Webster, the term “hippie,” in the sense of hirsute member of the counterculture, dates back to 1965, which is a skosh later than I might have guessed. One fun thing about dictionaries is that they’ll provide a date of introduction into written English for just about any word you can think of. This comes in awfully handy when you’re writing period fiction and wish to be era-appropriate, especially in dialogue. Copyediting a novel set during New York’s 1863 Draft Riots, I learned that what we now call a hangover”
Dreyer’s English: An Utterly Correct Guide to Clarity and Style