noun (n)

• lack of ability (especially mental ability) to do something(noun.cognition)

  Antonym:
  ability, power
  

  source: wordnet30
• lacking the power to perform(noun.attribute)

  Synonym:
  unfitness
  Antonym:
  ability
  

  source: wordnet30
• The quality or state of being unable; lack of ability; want of sufficient power, strength, resources, or capacity.(noun)

  source: webster1913