imbecility

nouns

retardation more severe than a moron but not as severe as an idiot
imbecility
is derived from
imbecile
is a type of (narrower)
lack of normal development of intellectual capacities
backwardness, mental retardation, retardation, slowness, subnormality
a stupid mistake
betise, folly, foolishness, imbecility, stupidity