noun (n)

• a poor ability to understand or to profit from experience(noun.cognition)

  Antonym:
  intelligence
  

  source: wordnet30
• a stupid mistake(noun.act)

  Synonym:
  betise, folly, foolishness, imbecility
  

  source: wordnet30
• The quality or state of being stupid; extreme dullness of perception or understanding; insensibility; sluggishness.(noun)

  source: webster1913