Green’s Dictionary of Slang

hippie n.2

also hippy
[like many terms, hippie crossed from the black to white worlds; unlike most, however, it altered its meaning, in this case from negative to, in peer-group eyes at least, positive. Since the 1960s/early 1970s the negative image has returned, although not as a failed hipster but as a 1960s throwback]

1. [1950s–60s] (US black) one who poses (with little or no success) as a hipster n.

2. [1950s–70s] (orig. US) a sophisticated, cool, ‘hip’ person.

3. [1960s+] (orig. US, also hippiehead) a (usu.) young person, preaching a philosophy of ‘love and peace’, backed by a wide spectrum of drug usage, esp. of cannabis and hallucinogens.