noun (n)

• any specific behavior(noun.act)

  Example:
  They avoided all recreational activity.
  

  Antonym:
  inactivity
  

  source: wordnet30
• the state of being active(noun.state)

  Example:
  His sphere of activity.
  

  Synonym:
  action, activeness
  Antonym:
  inaction, inactiveness, inactivity
  

  source: wordnet30
• an organic process that takes place in the body(noun.process)

  Example:
  Respiratory activity.
  

  Synonym:
  bodily function, bodily process, body process
  

  source: wordnet30
• (chemistry) the capacity of a substance to take part in a chemical reaction(noun.state)

  Example:
  Catalytic activity.
  

  source: wordnet30
• a process existing in or produced by nature (rather than by the intent of human beings)(noun.process)

  Example:
  Volcanic activity.
  

  Synonym:
  action, natural action, natural process
  

  source: wordnet30
• the trait of being active; moving or acting rapidly and energetically(noun.attribute)

  Example:
  The level of activity declines with age.
  

  Synonym:
  activeness
  Antonym:
  inactiveness, inactivity, inertia
  

  source: wordnet30
• The state or quality of being active; nimbleness; agility; vigorous action or operation; energy; active force; as, an increasing variety of human activities.(noun)

  source: webster1913