arrested development
backwardness
blithering idiocy
cretinism
half-wittedness
idiocy
idiotism
imbecility
infantilism
insanity
mental defectiveness
mental deficiency
mental handicap
mental retardation
mongolianism
mongolism
mongoloid idiocy
moronism
moronity
profound idiocy
retardation
retardment
simple-wittedness
simplemindedness
simpleness
simplicity
subnormality
slowness