Green’s Dictionary of Slang

hipster n.

also hepster
[hip adj. + -ster sfx; black use dropped by 1940s]

1. [1930s+] (orig. US black) one who espouses the fashionable Bohemian stance of the period; the essence was a conscious downplaying of emotional display, a stance poss. facilitated by heroin addiction.

2. [2000s+] in 21st century use, a liberal, culturally orientated youth cult for those under 30, often in creative occupations; seen as the current evocation of middle-class counter-cultural aspirations and fashions and praised or derided accordingly .