noun (n)

• required activity(noun.cognition)

  Example:
  The requirements of his work affected his health.
  

  Synonym:
  demand
  

  source: wordnet30
• anything indispensable(noun.object)

  Example:
  Allow farmers to buy their requirements under favorable conditions.
  

  Synonym:
  essential, necessary, necessity, requisite
  Antonym:
  inessential, nonessential
  

  source: wordnet30
• something that is required in advance(noun.cognition)

  Synonym:
  prerequisite
  

  source: wordnet30
• The act of requiring; demand; requisition.(noun)

  source: webster1913