WordNet (r) 3.0 (2006):

flower child
    n 1: someone who rejects the established culture; advocates
         extreme liberalism in politics and lifestyle [syn:
         hippie, hippy, hipster, flower child]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "flower child":
   Bohemian, beatnik, deviant, dissenter, dropout, freak, heretic,
   hippie, maverick, misfit, nonconformist, nonjuror, original,
   sectarian, sectary, swinger, ugly duckling, unconformist, yippie