noun (n)

• weakness characterized by a lack of vitality or energy(noun.attribute)

  Synonym:
  inanition, lassitude, lethargy
  

  source: wordnet30
• the quality of being loose (not taut)(noun.attribute)

  Example:
  He hadn't counted on the slackness of the rope.
  

  Synonym:
  slack
  

  source: wordnet30
• the quality of being lax and neglectful(noun.attribute)

  Synonym:
  laxity, laxness, remissness
  

  source: wordnet30
• The quality or state of being slack.(noun)

  source: webster1913