noun (n)

• any of various controls or devices for regulating or controlling fluid flow, pressure, temperature, etc.(noun.artifact)

  source: wordnet30
• an official responsible for control and supervision of a particular activity or area of public interest(noun.person)

  source: wordnet30
• a control that maintains a steady speed in a machine (as by controlling the supply of fuel)(noun.artifact)

  Synonym:
  governor
  

  source: wordnet30
• One who, or that which, regulates.(noun)

  source: webster1913