Wordnet 3.0
NOUN (2)
1. 
 someone who quits school before graduation; 
2. 
 someone who withdraws from a social group or environment; 
WordNet (r) 3.0 (2006):
dropout
    n 1: someone who quits school before graduation
    2: someone who withdraws from a social group or environment
Moby Thesaurus II by Grady Ward, 1.0:
19 Moby Thesaurus words for "dropout":
   Bohemian, beatnik, deviant, dissenter, flower child, freak,
   heretic, hippie, maverick, misfit, nonconformist, nonjuror,
   original, sectarian, sectary, swinger, ugly duckling, unconformist,
   yippie