WordNet (r) 3.0 (2006):

arrested development
    n 1: an abnormal state in which development has stopped
         prematurely [syn: arrested development, fixation,
         infantile fixation, regression]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "arrested development":
   Freudian fixation, amentia, backwardness, blithering idiocy,
   cretinism, father fixation, fixation, half-wittedness, idiocy,
   idiotism, imbecility, infantile fixation, infantilism, insanity,
   libido fixation, mental defectiveness, mental deficiency,
   mental handicap, mental retardation, mongolianism, mongolism,
   mongoloid idiocy, moronism, moronity, mother fixation,
   parent fixation, pregenital fixation, profound idiocy, regression,
   retardation, retardment, retreat to immaturity, simple-wittedness,
   simplemindedness, simpleness, simplicity, subnormality