noun (n)

• an occurrence of control or strength weakening(noun.event)

  Example:
  The loosening of his grip.
  

  Synonym:
  relaxation, slackening
  

  source: wordnet30
• the act of making something less tight(noun.act)

  Synonym:
  laxation
  Antonym:
  tightening
  

  source: wordnet30