WordNet (r) 3.0 (2006):

goon
    n 1: an awkward stupid person [syn: lout, clod,
         stumblebum, goon, oaf, lubber, lummox, lump,
         gawk]
    2: an aggressive and violent young criminal [syn: hood,
       hoodlum, goon, punk, thug, tough, toughie,
       strong-armer]